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 $26.80   11.389%   $29.8523   $29.85   $29.85   $29.90  
  Purchase #2 $239.39   9.429%   $261.9621   $261.96   $261.95   $262.00  
  Purchase #3 $85.39   7.632%   $91.907   $91.91   $91.90   $91.90  
  Purchase #4 $159.82   4.158%   $166.4653   $166.47   $166.45   $166.50  
  Purchase #5 $83.99   6.238%   $89.2293   $89.23   $89.25   $89.20  
  Purchase #6 $229.99   9.529%   $251.9057   $251.91   $251.90   $251.90  
  Purchase #7 $110.75   13.764%   $125.9936   $125.99   $126.00   $126.00  
  7 purchase totals = $936.13       $1,017.3153   $1,017.32   $1,017.30   $1,017.40