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 $54.32   10.386%   $59.9617   $59.96   $59.95   $60.00  
  Purchase #2 $134.45   10.562%   $148.6506   $148.65   $148.65   $148.70  
  Purchase #3 $242.36   4.214%   $252.5731   $252.57   $252.55   $252.60  
  Purchase #4 $207.48   11.298%   $230.9211   $230.92   $230.90   $230.90  
  Purchase #5 $191.94   3.355%   $198.3796   $198.38   $198.40   $198.40  
  Purchase #6 $5.64   4.127%   $5.8728   $5.87   $5.85   $5.90  
  Purchase #7 $217.80   5.171%   $229.0624   $229.06   $229.05   $229.10  
  7 purchase totals = $1,053.99       $1,125.4213   $1,125.41   $1,125.35   $1,125.60