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 $64.60   13.240%   $73.153   $73.15   $73.15   $73.20  
  Purchase #2 $233.47   6.751%   $249.2316   $249.23   $249.25   $249.20  
  Purchase #3 $153.63   10.507%   $169.7719   $169.77   $169.75   $169.80  
  Purchase #4 $250.68   5.673%   $264.9011   $264.90   $264.90   $264.90  
  Purchase #5 $12.65   13.520%   $14.3603   $14.36   $14.35   $14.40  
  Purchase #6 $98.56   8.214%   $106.6557   $106.66   $106.65   $106.70  
  Purchase #7 $27.64   8.622%   $30.0231   $30.02   $30.00   $30.00  
  7 purchase totals = $841.23       $908.0967   $908.09   $908.05   $908.20