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 $222.80   10.858%   $246.9916   $246.99   $247.00   $247.00  
  Purchase #2 $75.41   12.400%   $84.7608   $84.76   $84.75   $84.80  
  Purchase #3 $203.77   6.722%   $217.4674   $217.47   $217.45   $217.50  
  Purchase #4 $227.78   11.860%   $254.7947   $254.79   $254.80   $254.80  
  Purchase #5 $76.63   7.483%   $82.3642   $82.36   $82.35   $82.40  
  Purchase #6 $16.30   7.134%   $17.4628   $17.46   $17.45   $17.50  
  Purchase #7 $125.28   3.623%   $129.8189   $129.82   $129.80   $129.80  
  7 purchase totals = $947.97       $1,033.6604   $1,033.65   $1,033.60   $1,033.80