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 $236.38   11.119%   $262.6631   $262.66   $262.65   $262.70  
  Purchase #2 $74.69   13.282%   $84.6103   $84.61   $84.60   $84.60  
  Purchase #3 $87.79   3.639%   $90.9847   $90.98   $91.00   $91.00  
  Purchase #4 $166.84   9.827%   $183.2354   $183.24   $183.25   $183.20  
  Purchase #5 $203.65   8.864%   $221.7015   $221.70   $221.70   $221.70  
  Purchase #6 $8.96   12.628%   $10.0915   $10.09   $10.10   $10.10  
  Purchase #7 $93.65   8.871%   $101.9577   $101.96   $101.95   $102.00  
  7 purchase totals = $871.96       $955.2442   $955.24   $955.25   $955.30