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 $84.84   7.451%   $91.1614   $91.16   $91.15   $91.20  
  Purchase #2 $239.44   5.857%   $253.464   $253.46   $253.45   $253.50  
  Purchase #3 $59.53   5.406%   $62.7482   $62.75   $62.75   $62.70  
  Purchase #4 $200.85   4.847%   $210.5852   $210.59   $210.60   $210.60  
  Purchase #5 $156.80   4.165%   $163.3307   $163.33   $163.35   $163.30  
  Purchase #6 $205.43   3.806%   $213.2487   $213.25   $213.25   $213.20  
  Purchase #7 $49.72   3.834%   $51.6263   $51.63   $51.65   $51.60  
  7 purchase totals = $996.61       $1,046.1645   $1,046.17   $1,046.20   $1,046.10