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 $43.56   10.433%   $48.1046   $48.10   $48.10   $48.10  
  Purchase #2 $118.25   5.669%   $124.9536   $124.95   $124.95   $125.00  
  Purchase #3 $6.35   3.127%   $6.5486   $6.55   $6.55   $6.50  
  Purchase #4 $57.71   10.355%   $63.6859   $63.69   $63.70   $63.70  
  Purchase #5 $221.97   10.603%   $245.5055   $245.51   $245.50   $245.50  
  Purchase #6 $187.35   6.384%   $199.3104   $199.31   $199.30   $199.30  
  Purchase #7 $97.69   7.750%   $105.261   $105.26   $105.25   $105.30  
  7 purchase totals = $732.88       $793.3696   $793.37   $793.35   $793.40