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 $57.65   8.366%   $62.473   $62.47   $62.45   $62.50  
  Purchase #2 $80.54   9.617%   $88.2855   $88.29   $88.30   $88.30  
  Purchase #3 $196.55   4.517%   $205.4282   $205.43   $205.45   $205.40  
  Purchase #4 $131.87   7.445%   $141.6877   $141.69   $141.70   $141.70  
  Purchase #5 $153.49   9.204%   $167.6172   $167.62   $167.60   $167.60  
  Purchase #6 $182.55   10.165%   $201.1062   $201.11   $201.10   $201.10  
  Purchase #7 $95.50   7.131%   $102.3101   $102.31   $102.30   $102.30  
  7 purchase totals = $898.15       $968.9079   $968.92   $968.90   $968.90