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 $247.43   11.643%   $276.2383   $276.24   $276.25   $276.20  
  Purchase #2 $183.96   8.487%   $199.5727   $199.57   $199.55   $199.60  
  Purchase #3 $157.46   10.652%   $174.2326   $174.23   $174.25   $174.20  
  Purchase #4 $160.87   6.239%   $170.9067   $170.91   $170.90   $170.90  
  Purchase #5 $209.38   11.629%   $233.7288   $233.73   $233.75   $233.70  
  Purchase #6 $104.28   4.106%   $108.5617   $108.56   $108.55   $108.60  
  Purchase #7 $50.65   4.636%   $52.9981   $53.00   $53.00   $53.00  
  7 purchase totals = $1,114.03       $1,216.2389   $1,216.24   $1,216.25   $1,216.20