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 $196.96   8.577%   $213.8533   $213.85   $213.85   $213.90  
  Purchase #2 $167.41   13.496%   $190.0037   $190.00   $190.00   $190.00  
  Purchase #3 $245.77   4.804%   $257.5768   $257.58   $257.60   $257.60  
  Purchase #4 $101.54   10.643%   $112.3469   $112.35   $112.35   $112.30  
  Purchase #5 $212.95   5.538%   $224.7432   $224.74   $224.75   $224.70  
  Purchase #6 $203.67   12.214%   $228.5463   $228.55   $228.55   $228.50  
  Purchase #7 $198.71   13.420%   $225.3769   $225.38   $225.40   $225.40  
  7 purchase totals = $1,327.01       $1,452.4471   $1,452.45   $1,452.50   $1,452.40