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 $139.64   13.576%   $158.5975   $158.60   $158.60   $158.60  
  Purchase #2 $212.53   11.407%   $236.7733   $236.77   $236.75   $236.80  
  Purchase #3 $166.53   3.148%   $171.7724   $171.77   $171.75   $171.80  
  Purchase #4 $231.67   5.403%   $244.1871   $244.19   $244.20   $244.20  
  Purchase #5 $71.42   10.176%   $78.6877   $78.69   $78.70   $78.70  
  Purchase #6 $200.50   5.766%   $212.0608   $212.06   $212.05   $212.10  
  Purchase #7 $149.64   10.270%   $165.008   $165.01   $165.00   $165.00  
  7 purchase totals = $1,171.93       $1,267.0868   $1,267.09   $1,267.05   $1,267.20