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 $164.61   8.376%   $178.3977   $178.40   $178.40   $178.40  
  Purchase #2 $244.34   11.172%   $271.6377   $271.64   $271.65   $271.60  
  Purchase #3 $25.74   9.634%   $28.2198   $28.22   $28.20   $28.20  
  Purchase #4 $108.60   6.283%   $115.4233   $115.42   $115.40   $115.40  
  Purchase #5 $48.47   4.258%   $50.5339   $50.53   $50.55   $50.50  
  Purchase #6 $154.30   11.147%   $171.4998   $171.50   $171.50   $171.50  
  Purchase #7 $188.88   9.618%   $207.0465   $207.05   $207.05   $207.00  
  7 purchase totals = $934.94       $1,022.7587   $1,022.76   $1,022.75   $1,022.60