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 $41.79   11.861%   $46.7467   $46.75   $46.75   $46.70  
  Purchase #2 $29.41   8.570%   $31.9304   $31.93   $31.95   $31.90  
  Purchase #3 $188.32   12.554%   $211.9617   $211.96   $211.95   $212.00  
  Purchase #4 $84.27   13.412%   $95.5723   $95.57   $95.55   $95.60  
  Purchase #5 $87.82   10.712%   $97.2273   $97.23   $97.25   $97.20  
  Purchase #6 $248.32   13.405%   $281.6073   $281.61   $281.60   $281.60  
  Purchase #7 $121.40   9.230%   $132.6052   $132.61   $132.60   $132.60  
  7 purchase totals = $801.33       $897.6509   $897.66   $897.65   $897.60