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 $51.97   10.559%   $57.4575   $57.46   $57.45   $57.50  
  Purchase #2 $146.82   10.765%   $162.6252   $162.63   $162.65   $162.60  
  Purchase #3 $82.45   5.168%   $86.711   $86.71   $86.70   $86.70  
  Purchase #4 $45.43   10.834%   $50.3519   $50.35   $50.35   $50.40  
  Purchase #5 $206.92   6.262%   $219.8773   $219.88   $219.90   $219.90  
  Purchase #6 $193.93   8.548%   $210.5071   $210.51   $210.50   $210.50  
  Purchase #7 $115.63   13.152%   $130.8377   $130.84   $130.85   $130.80  
  7 purchase totals = $843.15       $918.3677   $918.38   $918.40   $918.40