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 $119.46   3.202%   $123.2851   $123.29   $123.30   $123.30  
  Purchase #2 $60.68   11.553%   $67.6904   $67.69   $67.70   $67.70  
  Purchase #3 $26.63   8.660%   $28.9362   $28.94   $28.95   $28.90  
  Purchase #4 $233.73   10.289%   $257.7785   $257.78   $257.80   $257.80  
  Purchase #5 $24.90   3.213%   $25.7   $25.70   $25.70   $25.70  
  Purchase #6 $212.96   6.662%   $227.1474   $227.15   $227.15   $227.10  
  Purchase #7 $139.31   8.356%   $150.9507   $150.95   $150.95   $151.00  
  7 purchase totals = $817.67       $881.4883   $881.50   $881.55   $881.50