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 $122.49   8.763%   $133.2238   $133.22   $133.20   $133.20  
  Purchase #2 $215.63   12.351%   $242.2625   $242.26   $242.25   $242.30  
  Purchase #3 $160.37   3.434%   $165.8771   $165.88   $165.90   $165.90  
  Purchase #4 $240.69   10.257%   $265.3776   $265.38   $265.40   $265.40  
  Purchase #5 $200.98   4.548%   $210.1206   $210.12   $210.10   $210.10  
  Purchase #6 $13.29   8.853%   $14.4666   $14.47   $14.45   $14.50  
  Purchase #7 $24.61   5.212%   $25.8927   $25.89   $25.90   $25.90  
  7 purchase totals = $978.06       $1,057.2209   $1,057.22   $1,057.20   $1,057.30