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 $205.26   12.559%   $231.0386   $231.04   $231.05   $231.00  
  Purchase #2 $169.69   8.527%   $184.1595   $184.16   $184.15   $184.20  
  Purchase #3 $45.81   6.436%   $48.7583   $48.76   $48.75   $48.80  
  Purchase #4 $108.73   5.775%   $115.0092   $115.01   $115.00   $115.00  
  Purchase #5 $170.62   10.165%   $187.9635   $187.96   $187.95   $188.00  
  Purchase #6 $166.53   11.823%   $186.2188   $186.22   $186.20   $186.20  
  Purchase #7 $119.28   4.759%   $124.9565   $124.96   $124.95   $125.00  
  7 purchase totals = $985.92       $1,078.1044   $1,078.11   $1,078.05   $1,078.20