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 $67.75   6.574%   $72.2039   $72.20   $72.20   $72.20  
  Purchase #2 $184.30   3.757%   $191.2242   $191.22   $191.20   $191.20  
  Purchase #3 $190.88   3.295%   $197.1695   $197.17   $197.15   $197.20  
  Purchase #4 $15.99   6.579%   $17.042   $17.04   $17.05   $17.00  
  Purchase #5 $45.94   4.212%   $47.875   $47.88   $47.90   $47.90  
  Purchase #6 $172.72   6.790%   $184.4477   $184.45   $184.45   $184.40  
  Purchase #7 $26.73   13.490%   $30.3359   $30.34   $30.35   $30.30  
  7 purchase totals = $704.31       $740.2982   $740.30   $740.30   $740.20