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 $58.95   7.423%   $63.3259   $63.33   $63.35   $63.30  
  Purchase #2 $100.75   3.190%   $103.9639   $103.96   $103.95   $104.00  
  Purchase #3 $101.34   5.102%   $106.5104   $106.51   $106.50   $106.50  
  Purchase #4 $112.86   9.656%   $123.7578   $123.76   $123.75   $123.80  
  Purchase #5 $213.76   6.187%   $226.9853   $226.99   $227.00   $227.00  
  Purchase #6 $245.42   8.352%   $265.9175   $265.92   $265.90   $265.90  
  Purchase #7 $94.60   5.749%   $100.0386   $100.04   $100.05   $100.00  
  7 purchase totals = $927.68       $990.4994   $990.51   $990.50   $990.50