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 $169.29   10.836%   $187.6343   $187.63   $187.65   $187.60  
  Purchase #2 $176.66   8.476%   $191.6337   $191.63   $191.65   $191.60  
  Purchase #3 $216.71   10.496%   $239.4559   $239.46   $239.45   $239.50  
  Purchase #4 $75.76   3.234%   $78.2101   $78.21   $78.20   $78.20  
  Purchase #5 $154.65   5.871%   $163.7295   $163.73   $163.75   $163.70  
  Purchase #6 $9.37   10.324%   $10.3374   $10.34   $10.35   $10.30  
  Purchase #7 $64.85   3.348%   $67.0212   $67.02   $67.00   $67.00  
  7 purchase totals = $867.29       $938.0221   $938.02   $938.05   $937.90