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 $155.46   11.648%   $173.568   $173.57   $173.55   $173.60  
  Purchase #2 $119.42   5.421%   $125.8938   $125.89   $125.90   $125.90  
  Purchase #3 $119.51   9.731%   $131.1395   $131.14   $131.15   $131.10  
  Purchase #4 $63.65   7.579%   $68.474   $68.47   $68.45   $68.50  
  Purchase #5 $36.97   12.164%   $41.467   $41.47   $41.45   $41.50  
  Purchase #6 $240.74   13.620%   $273.5288   $273.53   $273.55   $273.50  
  Purchase #7 $102.58   9.395%   $112.2174   $112.22   $112.20   $112.20  
  7 purchase totals = $838.33       $926.2885   $926.29   $926.25   $926.30