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 $86.66   6.571%   $92.3544   $92.35   $92.35   $92.40  
  Purchase #2 $64.71   9.274%   $70.7112   $70.71   $70.70   $70.70  
  Purchase #3 $243.67   8.113%   $263.4389   $263.44   $263.45   $263.40  
  Purchase #4 $231.43   9.378%   $253.1335   $253.13   $253.15   $253.10  
  Purchase #5 $242.45   7.787%   $261.3296   $261.33   $261.35   $261.30  
  Purchase #6 $14.61   4.633%   $15.2869   $15.29   $15.30   $15.30  
  Purchase #7 $39.50   12.560%   $44.4612   $44.46   $44.45   $44.50  
  7 purchase totals = $923.03       $1,000.7157   $1,000.71   $1,000.75   $1,000.70