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 $47.57   4.517%   $49.7187   $49.72   $49.70   $49.70  
  Purchase #2 $219.64   5.603%   $231.9464   $231.95   $231.95   $231.90  
  Purchase #3 $67.87   9.476%   $74.3014   $74.30   $74.30   $74.30  
  Purchase #4 $29.30   4.549%   $30.6329   $30.63   $30.65   $30.60  
  Purchase #5 $88.83   5.742%   $93.9306   $93.93   $93.95   $93.90  
  Purchase #6 $76.85   7.203%   $82.3855   $82.39   $82.40   $82.40  
  Purchase #7 $170.45   13.391%   $193.275   $193.28   $193.30   $193.30  
  7 purchase totals = $700.51       $756.1905   $756.20   $756.25   $756.10