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 $237.39   7.387%   $254.926   $254.93   $254.95   $254.90  
  Purchase #2 $119.87   10.620%   $132.6002   $132.60   $132.60   $132.60  
  Purchase #3 $14.95   10.273%   $16.4858   $16.49   $16.50   $16.50  
  Purchase #4 $152.86   6.614%   $162.9702   $162.97   $162.95   $163.00  
  Purchase #5 $50.93   6.119%   $54.0464   $54.05   $54.05   $54.00  
  Purchase #6 $33.46   9.259%   $36.5581   $36.56   $36.55   $36.60  
  Purchase #7 $149.97   7.153%   $160.6974   $160.70   $160.70   $160.70  
  7 purchase totals = $759.43       $818.2841   $818.30   $818.30   $818.30