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 $28.47   12.730%   $32.0942   $32.09   $32.10   $32.10  
  Purchase #2 $194.93   11.730%   $217.7953   $217.80   $217.80   $217.80  
  Purchase #3 $237.90   3.626%   $246.5263   $246.53   $246.55   $246.50  
  Purchase #4 $192.39   7.175%   $206.194   $206.19   $206.20   $206.20  
  Purchase #5 $71.90   6.149%   $76.3211   $76.32   $76.30   $76.30  
  Purchase #6 $89.69   13.763%   $102.034   $102.03   $102.05   $102.00  
  Purchase #7 $250.29   12.521%   $281.6288   $281.63   $281.65   $281.60  
  7 purchase totals = $1,065.57       $1,162.5937   $1,162.59   $1,162.65   $1,162.50