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 $73.50   11.823%   $82.1899   $82.19   $82.20   $82.20  
  Purchase #2 $121.39   12.537%   $136.6087   $136.61   $136.60   $136.60  
  Purchase #3 $166.91   4.255%   $174.012   $174.01   $174.00   $174.00  
  Purchase #4 $27.93   12.451%   $31.4076   $31.41   $31.40   $31.40  
  Purchase #5 $76.66   10.387%   $84.6227   $84.62   $84.60   $84.60  
  Purchase #6 $75.90   3.828%   $78.8055   $78.81   $78.80   $78.80  
  Purchase #7 $60.73   7.544%   $65.3115   $65.31   $65.30   $65.30  
  7 purchase totals = $603.02       $652.9579   $652.96   $652.90   $652.90