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 $67.85   7.658%   $73.046   $73.05   $73.05   $73.00  
  Purchase #2 $79.55   4.285%   $82.9587   $82.96   $82.95   $83.00  
  Purchase #3 $233.89   13.726%   $265.9937   $265.99   $266.00   $266.00  
  Purchase #4 $178.44   10.863%   $197.8239   $197.82   $197.80   $197.80  
  Purchase #5 $185.89   6.327%   $197.6513   $197.65   $197.65   $197.70  
  Purchase #6 $138.39   4.389%   $144.4639   $144.46   $144.45   $144.50  
  Purchase #7 $62.58   12.173%   $70.1979   $70.20   $70.20   $70.20  
  7 purchase totals = $946.59       $1,032.1354   $1,032.13   $1,032.10   $1,032.20