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 $55.96   8.212%   $60.5554   $60.56   $60.55   $60.60  
  Purchase #2 $20.40   9.516%   $22.3413   $22.34   $22.35   $22.30  
  Purchase #3 $97.42   7.605%   $104.8288   $104.83   $104.85   $104.80  
  Purchase #4 $163.86   3.189%   $169.0855   $169.09   $169.10   $169.10  
  Purchase #5 $10.30   8.657%   $11.1917   $11.19   $11.20   $11.20  
  Purchase #6 $98.76   6.246%   $104.9285   $104.93   $104.95   $104.90  
  Purchase #7 $67.99   6.764%   $72.5888   $72.59   $72.60   $72.60  
  7 purchase totals = $514.69       $545.5200   $545.53   $545.60   $545.50