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 $241.85   10.618%   $267.5296   $267.53   $267.55   $267.50  
  Purchase #2 $137.72   4.747%   $144.2576   $144.26   $144.25   $144.30  
  Purchase #3 $236.27   12.787%   $266.4818   $266.48   $266.50   $266.50  
  Purchase #4 $116.65   12.271%   $130.9641   $130.96   $130.95   $131.00  
  Purchase #5 $82.85   7.291%   $88.8906   $88.89   $88.90   $88.90  
  Purchase #6 $200.77   4.102%   $209.0056   $209.01   $209.00   $209.00  
  Purchase #7 $163.83   12.442%   $184.2137   $184.21   $184.20   $184.20  
  7 purchase totals = $1,179.94       $1,291.3430   $1,291.34   $1,291.35   $1,291.40