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 $68.65   11.581%   $76.6004   $76.60   $76.60   $76.60  
  Purchase #2 $84.32   4.168%   $87.8345   $87.83   $87.85   $87.80  
  Purchase #3 $120.85   4.223%   $125.9535   $125.95   $125.95   $126.00  
  Purchase #4 $88.49   11.589%   $98.7451   $98.75   $98.75   $98.70  
  Purchase #5 $31.53   9.790%   $34.6168   $34.62   $34.60   $34.60  
  Purchase #6 $160.87   7.613%   $173.117   $173.12   $173.10   $173.10  
  Purchase #7 $136.36   11.242%   $151.6896   $151.69   $151.70   $151.70  
  7 purchase totals = $691.07       $748.5569   $748.56   $748.55   $748.50