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 $55.38   12.584%   $62.349   $62.35   $62.35   $62.30  
  Purchase #2 $123.92   7.386%   $133.0727   $133.07   $133.05   $133.10  
  Purchase #3 $172.84   8.501%   $187.5331   $187.53   $187.55   $187.50  
  Purchase #4 $72.92   3.165%   $75.2279   $75.23   $75.25   $75.20  
  Purchase #5 $173.85   13.553%   $197.4119   $197.41   $197.40   $197.40  
  Purchase #6 $200.85   13.592%   $228.1495   $228.15   $228.15   $228.10  
  Purchase #7 $25.98   9.645%   $28.4858   $28.49   $28.50   $28.50  
  7 purchase totals = $825.74       $912.2299   $912.23   $912.25   $912.10