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 $245.64   10.833%   $272.2502   $272.25   $272.25   $272.30  
  Purchase #2 $134.98   11.677%   $150.7416   $150.74   $150.75   $150.70  
  Purchase #3 $88.62   6.621%   $94.4875   $94.49   $94.50   $94.50  
  Purchase #4 $166.30   3.576%   $172.2469   $172.25   $172.25   $172.20  
  Purchase #5 $154.54   10.491%   $170.7528   $170.75   $170.75   $170.80  
  Purchase #6 $134.38   5.449%   $141.7024   $141.70   $141.70   $141.70  
  Purchase #7 $240.87   5.352%   $253.7614   $253.76   $253.75   $253.80  
  7 purchase totals = $1,165.33       $1,255.9428   $1,255.94   $1,255.95   $1,256.00