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 $60.58   12.308%   $68.0362   $68.04   $68.05   $68.00  
  Purchase #2 $145.87   7.428%   $156.7052   $156.71   $156.70   $156.70  
  Purchase #3 $183.87   3.826%   $190.9049   $190.90   $190.90   $190.90  
  Purchase #4 $73.90   8.600%   $80.2554   $80.26   $80.25   $80.30  
  Purchase #5 $12.48   13.313%   $14.1415   $14.14   $14.15   $14.10  
  Purchase #6 $141.38   4.577%   $147.851   $147.85   $147.85   $147.90  
  Purchase #7 $249.94   3.226%   $258.0031   $258.00   $258.00   $258.00  
  7 purchase totals = $868.02       $915.8973   $915.90   $915.90   $915.90