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 $24.95   4.427%   $26.0545   $26.05   $26.05   $26.10  
  Purchase #2 $216.82   11.784%   $242.3701   $242.37   $242.35   $242.40  
  Purchase #3 $124.42   10.588%   $137.5936   $137.59   $137.60   $137.60  
  Purchase #4 $228.79   9.663%   $250.898   $250.90   $250.90   $250.90  
  Purchase #5 $44.98   11.256%   $50.0429   $50.04   $50.05   $50.00  
  Purchase #6 $151.73   11.643%   $169.3959   $169.40   $169.40   $169.40  
  Purchase #7 $60.78   10.610%   $67.2288   $67.23   $67.25   $67.20  
  7 purchase totals = $852.47       $943.5838   $943.58   $943.60   $943.60