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 $53.41   13.742%   $60.7496   $60.75   $60.75   $60.70  
  Purchase #2 $209.86   8.717%   $228.1535   $228.15   $228.15   $228.20  
  Purchase #3 $97.94   7.211%   $105.0025   $105.00   $105.00   $105.00  
  Purchase #4 $149.72   3.180%   $154.4811   $154.48   $154.50   $154.50  
  Purchase #5 $223.90   11.857%   $250.4478   $250.45   $250.45   $250.40  
  Purchase #6 $240.50   13.505%   $272.9795   $272.98   $273.00   $273.00  
  Purchase #7 $225.42   7.306%   $241.8892   $241.89   $241.90   $241.90  
  7 purchase totals = $1,200.75       $1,313.7032   $1,313.70   $1,313.75   $1,313.70