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 $222.96   8.466%   $241.8358   $241.84   $241.85   $241.80  
  Purchase #2 $21.66   13.176%   $24.5139   $24.51   $24.50   $24.50  
  Purchase #3 $58.90   12.513%   $66.2702   $66.27   $66.25   $66.30  
  Purchase #4 $183.88   10.396%   $202.9962   $203.00   $203.00   $203.00  
  Purchase #5 $43.30   6.713%   $46.2067   $46.21   $46.20   $46.20  
  Purchase #6 $75.75   12.613%   $85.3043   $85.30   $85.30   $85.30  
  Purchase #7 $86.85   8.845%   $94.5319   $94.53   $94.55   $94.50  
  7 purchase totals = $693.30       $761.6590   $761.66   $761.65   $761.60