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 $226.73   8.204%   $245.3309   $245.33   $245.35   $245.30  
  Purchase #2 $130.39   7.427%   $140.0741   $140.07   $140.05   $140.10  
  Purchase #3 $160.92   3.790%   $167.0189   $167.02   $167.00   $167.00  
  Purchase #4 $194.92   11.631%   $217.5911   $217.59   $217.60   $217.60  
  Purchase #5 $207.68   12.735%   $234.128   $234.13   $234.15   $234.10  
  Purchase #6 $244.80   6.198%   $259.9727   $259.97   $259.95   $260.00  
  Purchase #7 $172.68   7.274%   $185.2407   $185.24   $185.25   $185.20  
  7 purchase totals = $1,338.12       $1,449.3564   $1,449.35   $1,449.35   $1,449.30