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 $86.34   13.339%   $97.8569   $97.86   $97.85   $97.90  
  Purchase #2 $9.36   13.261%   $10.6012   $10.60   $10.60   $10.60  
  Purchase #3 $50.28   12.552%   $56.5911   $56.59   $56.60   $56.60  
  Purchase #4 $244.76   10.761%   $271.0986   $271.10   $271.10   $271.10  
  Purchase #5 $56.78   7.124%   $60.825   $60.83   $60.85   $60.80  
  Purchase #6 $203.88   5.823%   $215.7519   $215.75   $215.75   $215.80  
  Purchase #7 $159.65   9.684%   $175.1105   $175.11   $175.10   $175.10  
  7 purchase totals = $811.05       $887.8352   $887.84   $887.85   $887.90