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 $218.28   13.596%   $247.9573   $247.96   $247.95   $248.00  
  Purchase #2 $230.97   10.230%   $254.5982   $254.60   $254.60   $254.60  
  Purchase #3 $69.28   9.309%   $75.7293   $75.73   $75.75   $75.70  
  Purchase #4 $217.85   8.642%   $236.6766   $236.68   $236.70   $236.70  
  Purchase #5 $151.68   9.586%   $166.22   $166.22   $166.20   $166.20  
  Purchase #6 $147.95   4.586%   $154.735   $154.74   $154.75   $154.70  
  Purchase #7 $233.96   9.601%   $256.4225   $256.42   $256.40   $256.40  
  7 purchase totals = $1,269.97       $1,392.3389   $1,392.35   $1,392.35   $1,392.30