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 $228.73   10.629%   $253.0417   $253.04   $253.05   $253.00  
  Purchase #2 $29.36   4.829%   $30.7778   $30.78   $30.80   $30.80  
  Purchase #3 $184.44   8.245%   $199.6471   $199.65   $199.65   $199.60  
  Purchase #4 $86.42   12.373%   $97.1127   $97.11   $97.10   $97.10  
  Purchase #5 $169.70   11.233%   $188.7624   $188.76   $188.75   $188.80  
  Purchase #6 $80.79   3.244%   $83.4108   $83.41   $83.40   $83.40  
  Purchase #7 $104.51   5.271%   $110.0187   $110.02   $110.00   $110.00  
  7 purchase totals = $883.95       $962.7712   $962.77   $962.75   $962.70