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 $68.69   12.777%   $77.4665   $77.47   $77.45   $77.50  
  Purchase #2 $145.73   8.326%   $157.8635   $157.86   $157.85   $157.90  
  Purchase #3 $87.80   7.791%   $94.6405   $94.64   $94.65   $94.60  
  Purchase #4 $129.97   11.294%   $144.6488   $144.65   $144.65   $144.60  
  Purchase #5 $54.75   5.819%   $57.9359   $57.94   $57.95   $57.90  
  Purchase #6 $149.58   13.389%   $169.6073   $169.61   $169.60   $169.60  
  Purchase #7 $221.29   9.123%   $241.4783   $241.48   $241.50   $241.50  
  7 purchase totals = $857.81       $943.6408   $943.65   $943.65   $943.60