Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $58.56   6.398%   $62.3067   $62.31   $62.30   $62.30  
  Purchase #2 $212.38   12.745%   $239.4478   $239.45   $239.45   $239.40  
  Purchase #3 $119.46   11.212%   $132.8539   $132.85   $132.85   $132.90  
  Purchase #4 $229.64   10.618%   $254.0232   $254.02   $254.00   $254.00  
  Purchase #5 $168.48   13.371%   $191.0075   $191.01   $191.00   $191.00  
  Purchase #6 $196.72   11.553%   $219.4471   $219.45   $219.45   $219.40  
  Purchase #7 $246.64   12.268%   $276.8978   $276.90   $276.90   $276.90  
  7 purchase totals = $1,231.88       $1,375.9840   $1,375.99   $1,375.95   $1,375.90