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 $68.99   12.559%   $77.6545   $77.65   $77.65   $77.70  
  Purchase #2 $229.91   6.395%   $244.6127   $244.61   $244.60   $244.60  
  Purchase #3 $101.40   13.352%   $114.9389   $114.94   $114.95   $114.90  
  Purchase #4 $152.46   7.800%   $164.3519   $164.35   $164.35   $164.40  
  Purchase #5 $179.99   7.287%   $193.1059   $193.11   $193.10   $193.10  
  Purchase #6 $95.72   3.324%   $98.9017   $98.90   $98.90   $98.90  
  Purchase #7 $67.35   11.516%   $75.106   $75.11   $75.10   $75.10  
  7 purchase totals = $895.82       $968.6716   $968.67   $968.65   $968.70