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 $234.35   8.194%   $253.5526   $253.55   $253.55   $253.60  
  Purchase #2 $142.73   10.659%   $157.9436   $157.94   $157.95   $157.90  
  Purchase #3 $71.47   7.237%   $76.6423   $76.64   $76.65   $76.60  
  Purchase #4 $12.62   12.549%   $14.2037   $14.20   $14.20   $14.20  
  Purchase #5 $65.53   9.807%   $71.9565   $71.96   $71.95   $72.00  
  Purchase #6 $248.93   11.137%   $276.6533   $276.65   $276.65   $276.70  
  Purchase #7 $23.51   8.396%   $25.4839   $25.48   $25.50   $25.50  
  7 purchase totals = $799.14       $876.4359   $876.42   $876.45   $876.50