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 $57.81   13.791%   $65.7826   $65.78   $65.80   $65.80  
  Purchase #2 $219.68   9.733%   $241.0615   $241.06   $241.05   $241.10  
  Purchase #3 $83.32   11.605%   $92.9893   $92.99   $93.00   $93.00  
  Purchase #4 $240.30   13.613%   $273.012   $273.01   $273.00   $273.00  
  Purchase #5 $100.43   5.346%   $105.799   $105.80   $105.80   $105.80  
  Purchase #6 $25.33   6.274%   $26.9192   $26.92   $26.90   $26.90  
  Purchase #7 $219.54   7.752%   $236.5587   $236.56   $236.55   $236.60  
  7 purchase totals = $946.41       $1,042.1223   $1,042.12   $1,042.10   $1,042.20