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 $68.62   3.609%   $71.0965   $71.10   $71.10   $71.10  
  Purchase #2 $95.56   5.212%   $100.5406   $100.54   $100.55   $100.50  
  Purchase #3 $140.64   13.533%   $159.6728   $159.67   $159.65   $159.70  
  Purchase #4 $235.65   9.561%   $258.1805   $258.18   $258.20   $258.20  
  Purchase #5 $51.57   3.526%   $53.3884   $53.39   $53.40   $53.40  
  Purchase #6 $192.85   12.394%   $216.7518   $216.75   $216.75   $216.80  
  Purchase #7 $126.36   4.536%   $132.0917   $132.09   $132.10   $132.10  
  7 purchase totals = $911.25       $991.7223   $991.72   $991.75   $991.80