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 $63.26   4.677%   $66.2187   $66.22   $66.20   $66.20  
  Purchase #2 $65.91   11.673%   $73.6037   $73.60   $73.60   $73.60  
  Purchase #3 $179.61   9.731%   $197.0878   $197.09   $197.10   $197.10  
  Purchase #4 $37.87   13.455%   $42.9654   $42.97   $42.95   $43.00  
  Purchase #5 $167.88   8.777%   $182.6148   $182.61   $182.60   $182.60  
  Purchase #6 $91.40   10.403%   $100.9083   $100.91   $100.90   $100.90  
  Purchase #7 $244.84   9.409%   $267.877   $267.88   $267.90   $267.90  
  7 purchase totals = $850.77       $931.2757   $931.28   $931.25   $931.30