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 $244.32   9.556%   $267.6672   $267.67   $267.65   $267.70  
  Purchase #2 $163.37   10.552%   $180.6088   $180.61   $180.60   $180.60  
  Purchase #3 $246.38   11.546%   $274.827   $274.83   $274.85   $274.80  
  Purchase #4 $25.77   7.463%   $27.6932   $27.69   $27.70   $27.70  
  Purchase #5 $12.33   5.242%   $12.9763   $12.98   $13.00   $13.00  
  Purchase #6 $48.44   10.717%   $53.6313   $53.63   $53.65   $53.60  
  Purchase #7 $132.27   8.322%   $143.2775   $143.28   $143.30   $143.30  
  7 purchase totals = $872.88       $960.6813   $960.69   $960.75   $960.70