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 $214.34   6.156%   $227.5348   $227.53   $227.55   $227.50  
  Purchase #2 $121.62   3.858%   $126.3121   $126.31   $126.30   $126.30  
  Purchase #3 $6.55   10.177%   $7.2166   $7.22   $7.20   $7.20  
  Purchase #4 $63.53   6.370%   $67.5769   $67.58   $67.60   $67.60  
  Purchase #5 $235.29   10.383%   $259.7202   $259.72   $259.70   $259.70  
  Purchase #6 $100.89   3.569%   $104.4908   $104.49   $104.50   $104.50  
  Purchase #7 $246.71   5.506%   $260.2939   $260.29   $260.30   $260.30  
  7 purchase totals = $988.93       $1,053.1453   $1,053.14   $1,053.15   $1,053.10