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 $208.74   7.613%   $224.6314   $224.63   $224.65   $224.60  
  Purchase #2 $246.72   8.218%   $266.9954   $267.00   $267.00   $267.00  
  Purchase #3 $79.89   10.602%   $88.3599   $88.36   $88.35   $88.40  
  Purchase #4 $119.37   11.614%   $133.2336   $133.23   $133.25   $133.20  
  Purchase #5 $34.38   7.747%   $37.0434   $37.04   $37.05   $37.00  
  Purchase #6 $23.54   11.830%   $26.3248   $26.32   $26.30   $26.30  
  Purchase #7 $208.99   8.490%   $226.7333   $226.73   $226.75   $226.70  
  7 purchase totals = $921.63       $1,003.3218   $1,003.31   $1,003.35   $1,003.20