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 $90.79   6.157%   $96.3799   $96.38   $96.40   $96.40  
  Purchase #2 $101.28   3.493%   $104.8177   $104.82   $104.80   $104.80  
  Purchase #3 $9.85   11.854%   $11.0176   $11.02   $11.00   $11.00  
  Purchase #4 $209.38   11.227%   $232.8871   $232.89   $232.90   $232.90  
  Purchase #5 $184.70   8.234%   $199.9082   $199.91   $199.90   $199.90  
  Purchase #6 $35.33   12.217%   $39.6463   $39.65   $39.65   $39.60  
  Purchase #7 $114.40   3.497%   $118.4006   $118.40   $118.40   $118.40  
  7 purchase totals = $745.73       $803.0574   $803.07   $803.05   $803.00