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 $24.29   8.747%   $26.4146   $26.41   $26.40   $26.40  
  Purchase #2 $144.83   11.834%   $161.9692   $161.97   $161.95   $162.00  
  Purchase #3 $199.89   8.733%   $217.3464   $217.35   $217.35   $217.30  
  Purchase #4 $78.66   11.824%   $87.9608   $87.96   $87.95   $88.00  
  Purchase #5 $103.39   11.372%   $115.1475   $115.15   $115.15   $115.10  
  Purchase #6 $89.51   10.683%   $99.0724   $99.07   $99.05   $99.10  
  Purchase #7 $221.75   8.702%   $241.0467   $241.05   $241.05   $241.00  
  7 purchase totals = $862.32       $948.9576   $948.96   $948.90   $948.90