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 $54.85   6.303%   $58.3072   $58.31   $58.30   $58.30  
  Purchase #2 $194.89   6.624%   $207.7995   $207.80   $207.80   $207.80  
  Purchase #3 $183.29   10.696%   $202.8947   $202.89   $202.90   $202.90  
  Purchase #4 $178.51   11.748%   $199.4814   $199.48   $199.50   $199.50  
  Purchase #5 $14.67   10.533%   $16.2152   $16.22   $16.20   $16.20  
  Purchase #6 $136.48   8.770%   $148.4493   $148.45   $148.45   $148.40  
  Purchase #7 $222.76   6.306%   $236.8072   $236.81   $236.80   $236.80  
  7 purchase totals = $985.45       $1,069.9545   $1,069.96   $1,069.95   $1,069.90