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 $29.87   5.709%   $31.5753   $31.58   $31.60   $31.60  
  Purchase #2 $121.99   12.548%   $137.2973   $137.30   $137.30   $137.30  
  Purchase #3 $109.62   10.491%   $121.1202   $121.12   $121.10   $121.10  
  Purchase #4 $19.71   11.468%   $21.9703   $21.97   $21.95   $22.00  
  Purchase #5 $9.48   8.714%   $10.3061   $10.31   $10.30   $10.30  
  Purchase #6 $31.78   9.256%   $34.7216   $34.72   $34.70   $34.70  
  Purchase #7 $97.53   3.109%   $100.5622   $100.56   $100.55   $100.60  
  7 purchase totals = $419.98       $457.5530   $457.56   $457.50   $457.60