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 $39.31   10.161%   $43.3043   $43.30   $43.30   $43.30  
  Purchase #2 $232.32   8.362%   $251.7466   $251.75   $251.75   $251.70  
  Purchase #3 $31.42   3.734%   $32.5932   $32.59   $32.60   $32.60  
  Purchase #4 $124.99   6.804%   $133.4943   $133.49   $133.50   $133.50  
  Purchase #5 $198.37   6.491%   $211.2462   $211.25   $211.25   $211.20  
  Purchase #6 $49.46   3.116%   $51.0012   $51.00   $51.00   $51.00  
  Purchase #7 $58.32   7.811%   $62.8754   $62.88   $62.90   $62.90  
  7 purchase totals = $734.19       $786.2612   $786.26   $786.30   $786.20