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 $95.82   7.247%   $102.7641   $102.76   $102.75   $102.80  
  Purchase #2 $213.26   3.343%   $220.3893   $220.39   $220.40   $220.40  
  Purchase #3 $64.47   10.570%   $71.2845   $71.28   $71.30   $71.30  
  Purchase #4 $233.44   4.866%   $244.7992   $244.80   $244.80   $244.80  
  Purchase #5 $33.90   13.865%   $38.6002   $38.60   $38.60   $38.60  
  Purchase #6 $37.55   8.222%   $40.6374   $40.64   $40.65   $40.60  
  Purchase #7 $73.84   3.252%   $76.2413   $76.24   $76.25   $76.20  
  7 purchase totals = $752.28       $794.7160   $794.71   $794.75   $794.70