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 $221.72   11.335%   $246.852   $246.85   $246.85   $246.90  
  Purchase #2 $215.89   5.109%   $226.9198   $226.92   $226.90   $226.90  
  Purchase #3 $58.83   9.857%   $64.6289   $64.63   $64.65   $64.60  
  Purchase #4 $12.96   5.338%   $13.6518   $13.65   $13.65   $13.70  
  Purchase #5 $132.71   3.472%   $137.3177   $137.32   $137.30   $137.30  
  Purchase #6 $250.69   8.428%   $271.8182   $271.82   $271.80   $271.80  
  Purchase #7 $91.97   11.275%   $102.3396   $102.34   $102.35   $102.30  
  7 purchase totals = $984.77       $1,063.5280   $1,063.53   $1,063.50   $1,063.50