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 $60.55   9.827%   $66.5002   $66.50   $66.50   $66.50  
  Purchase #2 $93.32   5.658%   $98.6   $98.60   $98.60   $98.60  
  Purchase #3 $65.32   9.178%   $71.3151   $71.32   $71.30   $71.30  
  Purchase #4 $208.53   7.763%   $224.7182   $224.72   $224.70   $224.70  
  Purchase #5 $27.47   12.504%   $30.9048   $30.90   $30.90   $30.90  
  Purchase #6 $173.52   4.293%   $180.9692   $180.97   $180.95   $181.00  
  Purchase #7 $246.83   11.812%   $275.9856   $275.99   $276.00   $276.00  
  7 purchase totals = $875.54       $948.9931   $949.00   $948.95   $949.00