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 $203.26   10.672%   $224.9519   $224.95   $224.95   $225.00  
  Purchase #2 $54.56   11.109%   $60.6211   $60.62   $60.60   $60.60  
  Purchase #3 $132.59   13.396%   $150.3518   $150.35   $150.35   $150.40  
  Purchase #4 $208.71   5.715%   $220.6378   $220.64   $220.65   $220.60  
  Purchase #5 $84.46   3.503%   $87.4186   $87.42   $87.40   $87.40  
  Purchase #6 $245.62   6.169%   $260.7723   $260.77   $260.75   $260.80  
  Purchase #7 $229.51   7.387%   $246.4639   $246.46   $246.45   $246.50  
  7 purchase totals = $1,158.71       $1,251.2174   $1,251.21   $1,251.15   $1,251.30