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 $92.65   6.293%   $98.4805   $98.48   $98.50   $98.50  
  Purchase #2 $229.58   6.825%   $245.2488   $245.25   $245.25   $245.20  
  Purchase #3 $206.84   10.847%   $229.2759   $229.28   $229.30   $229.30  
  Purchase #4 $86.73   13.617%   $98.54   $98.54   $98.55   $98.50  
  Purchase #5 $233.29   3.539%   $241.5461   $241.55   $241.55   $241.50  
  Purchase #6 $65.38   4.441%   $68.2835   $68.28   $68.30   $68.30  
  Purchase #7 $123.93   9.331%   $135.4939   $135.49   $135.50   $135.50  
  7 purchase totals = $1,038.40       $1,116.8687   $1,116.87   $1,116.95   $1,116.80