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 $9.85   7.727%   $10.6111   $10.61   $10.60   $10.60  
  Purchase #2 $75.95   8.428%   $82.3511   $82.35   $82.35   $82.40  
  Purchase #3 $118.69   6.463%   $126.3609   $126.36   $126.35   $126.40  
  Purchase #4 $178.39   9.538%   $195.4048   $195.40   $195.40   $195.40  
  Purchase #5 $6.32   5.767%   $6.6845   $6.68   $6.70   $6.70  
  Purchase #6 $208.94   8.463%   $226.6226   $226.62   $226.60   $226.60  
  Purchase #7 $92.86   4.118%   $96.684   $96.68   $96.70   $96.70  
  7 purchase totals = $691.00       $744.7190   $744.70   $744.70   $744.80