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 $114.25   8.786%   $124.288   $124.29   $124.30   $124.30  
  Purchase #2 $85.37   8.857%   $92.9312   $92.93   $92.95   $92.90  
  Purchase #3 $164.31   6.847%   $175.5603   $175.56   $175.55   $175.60  
  Purchase #4 $220.63   9.127%   $240.7669   $240.77   $240.75   $240.80  
  Purchase #5 $81.35   4.712%   $85.1832   $85.18   $85.20   $85.20  
  Purchase #6 $53.74   8.156%   $58.123   $58.12   $58.10   $58.10  
  Purchase #7 $44.79   10.237%   $49.3752   $49.38   $49.40   $49.40  
  7 purchase totals = $764.44       $826.2278   $826.23   $826.25   $826.30