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 $24.25   9.505%   $26.555   $26.56   $26.55   $26.60  
  Purchase #2 $59.94   12.416%   $67.3822   $67.38   $67.40   $67.40  
  Purchase #3 $108.25   6.594%   $115.388   $115.39   $115.40   $115.40  
  Purchase #4 $245.99   4.559%   $257.2047   $257.20   $257.20   $257.20  
  Purchase #5 $242.38   9.652%   $265.7745   $265.77   $265.75   $265.80  
  Purchase #6 $229.40   13.458%   $260.2727   $260.27   $260.25   $260.30  
  Purchase #7 $13.29   7.682%   $14.3109   $14.31   $14.30   $14.30  
  7 purchase totals = $923.50       $1,006.8880   $1,006.88   $1,006.85   $1,007.00