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 $212.60   13.436%   $241.1649   $241.16   $241.15   $241.20  
  Purchase #2 $134.83   8.339%   $146.0735   $146.07   $146.05   $146.10  
  Purchase #3 $110.40   4.734%   $115.6263   $115.63   $115.65   $115.60  
  Purchase #4 $182.97   7.281%   $196.292   $196.29   $196.30   $196.30  
  Purchase #5 $130.58   11.439%   $145.517   $145.52   $145.50   $145.50  
  Purchase #6 $158.77   13.197%   $179.7229   $179.72   $179.70   $179.70  
  Purchase #7 $6.38   3.371%   $6.5951   $6.60   $6.60   $6.60  
  7 purchase totals = $936.53       $1,030.9917   $1,030.99   $1,030.95   $1,031.00