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 $84.81   12.752%   $95.625   $95.63   $95.65   $95.60  
  Purchase #2 $183.73   12.387%   $206.4886   $206.49   $206.50   $206.50  
  Purchase #3 $35.47   5.273%   $37.3403   $37.34   $37.35   $37.30  
  Purchase #4 $27.51   4.427%   $28.7279   $28.73   $28.75   $28.70  
  Purchase #5 $236.63   12.151%   $265.3829   $265.38   $265.40   $265.40  
  Purchase #6 $156.93   9.449%   $171.7583   $171.76   $171.75   $171.80  
  Purchase #7 $120.57   12.438%   $135.5665   $135.57   $135.55   $135.60  
  7 purchase totals = $845.65       $940.8895   $940.90   $940.95   $940.90