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 $60.94   9.120%   $66.4977   $66.50   $66.50   $66.50  
  Purchase #2 $98.51   7.822%   $106.2155   $106.22   $106.20   $106.20  
  Purchase #3 $57.94   8.491%   $62.8597   $62.86   $62.85   $62.90  
  Purchase #4 $235.88   9.598%   $258.5198   $258.52   $258.50   $258.50  
  Purchase #5 $151.90   3.705%   $157.5279   $157.53   $157.55   $157.50  
  Purchase #6 $229.39   9.453%   $251.0742   $251.07   $251.05   $251.10  
  Purchase #7 $57.49   8.320%   $62.2732   $62.27   $62.25   $62.30  
  7 purchase totals = $892.05       $964.9680   $964.97   $964.90   $965.00