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 $45.36   13.735%   $51.5902   $51.59   $51.60   $51.60  
  Purchase #2 $110.62   7.536%   $118.9563   $118.96   $118.95   $119.00  
  Purchase #3 $116.38   6.612%   $124.075   $124.08   $124.10   $124.10  
  Purchase #4 $216.54   11.338%   $241.0913   $241.09   $241.10   $241.10  
  Purchase #5 $233.63   7.319%   $250.7294   $250.73   $250.75   $250.70  
  Purchase #6 $64.55   5.786%   $68.2849   $68.28   $68.30   $68.30  
  Purchase #7 $16.93   10.765%   $18.7525   $18.75   $18.75   $18.80  
  7 purchase totals = $804.01       $873.4796   $873.48   $873.55   $873.60