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 $58.49   3.565%   $60.5752   $60.58   $60.60   $60.60  
  Purchase #2 $10.72   7.526%   $11.5268   $11.53   $11.55   $11.50  
  Purchase #3 $85.42   6.302%   $90.8032   $90.80   $90.80   $90.80  
  Purchase #4 $137.43   11.613%   $153.3897   $153.39   $153.40   $153.40  
  Purchase #5 $127.83   8.388%   $138.5524   $138.55   $138.55   $138.60  
  Purchase #6 $153.48   10.527%   $169.6368   $169.64   $169.65   $169.60  
  Purchase #7 $162.36   11.440%   $180.934   $180.93   $180.95   $180.90  
  7 purchase totals = $735.73       $805.4181   $805.42   $805.50   $805.40