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 $95.40   12.353%   $107.1848   $107.18   $107.20   $107.20  
  Purchase #2 $104.37   13.856%   $118.8315   $118.83   $118.85   $118.80  
  Purchase #3 $45.67   13.774%   $51.9606   $51.96   $51.95   $52.00  
  Purchase #4 $244.59   6.413%   $260.2756   $260.28   $260.30   $260.30  
  Purchase #5 $10.78   5.168%   $11.3371   $11.34   $11.35   $11.30  
  Purchase #6 $57.82   10.735%   $64.027   $64.03   $64.05   $64.00  
  Purchase #7 $96.99   6.226%   $103.0286   $103.03   $103.05   $103.00  
  7 purchase totals = $655.62       $716.6452   $716.65   $716.75   $716.60