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 $204.67   3.736%   $212.3165   $212.32   $212.30   $212.30  
  Purchase #2 $220.76   8.667%   $239.8933   $239.89   $239.90   $239.90  
  Purchase #3 $233.73   12.304%   $262.4881   $262.49   $262.50   $262.50  
  Purchase #4 $53.81   8.775%   $58.5318   $58.53   $58.55   $58.50  
  Purchase #5 $118.47   5.793%   $125.333   $125.33   $125.35   $125.30  
  Purchase #6 $173.54   9.636%   $190.2623   $190.26   $190.25   $190.30  
  Purchase #7 $50.37   4.848%   $52.8119   $52.81   $52.80   $52.80  
  7 purchase totals = $1,055.35       $1,141.6369   $1,141.63   $1,141.65   $1,141.60