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 $224.77   9.512%   $246.1501   $246.15   $246.15   $246.20  
  Purchase #2 $153.86   12.208%   $172.6432   $172.64   $172.65   $172.60  
  Purchase #3 $99.31   13.390%   $112.6076   $112.61   $112.60   $112.60  
  Purchase #4 $27.90   5.509%   $29.437   $29.44   $29.45   $29.40  
  Purchase #5 $62.99   12.103%   $70.6137   $70.61   $70.60   $70.60  
  Purchase #6 $161.68   11.169%   $179.738   $179.74   $179.75   $179.70  
  Purchase #7 $50.46   9.649%   $55.3289   $55.33   $55.35   $55.30  
  7 purchase totals = $780.97       $866.5185   $866.52   $866.55   $866.40