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 $41.66   3.667%   $43.1877   $43.19   $43.20   $43.20  
  Purchase #2 $164.33   9.836%   $180.4935   $180.49   $180.50   $180.50  
  Purchase #3 $91.39   6.689%   $97.5031   $97.50   $97.50   $97.50  
  Purchase #4 $71.75   9.493%   $78.5612   $78.56   $78.55   $78.60  
  Purchase #5 $80.97   8.374%   $87.7504   $87.75   $87.75   $87.80  
  Purchase #6 $10.61   12.545%   $11.941   $11.94   $11.95   $11.90  
  Purchase #7 $162.48   7.393%   $174.4921   $174.49   $174.50   $174.50  
  7 purchase totals = $623.19       $673.9290   $673.92   $673.95   $674.00