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 $228.67   13.105%   $258.6372   $258.64   $258.65   $258.60  
  Purchase #2 $169.59   3.428%   $175.4035   $175.40   $175.40   $175.40  
  Purchase #3 $155.95   13.439%   $176.9081   $176.91   $176.90   $176.90  
  Purchase #4 $110.35   5.561%   $116.4866   $116.49   $116.50   $116.50  
  Purchase #5 $154.90   3.271%   $159.9668   $159.97   $159.95   $160.00  
  Purchase #6 $24.53   8.120%   $26.5218   $26.52   $26.50   $26.50  
  Purchase #7 $147.54   4.871%   $154.7267   $154.73   $154.75   $154.70  
  7 purchase totals = $991.53       $1,068.6507   $1,068.66   $1,068.65   $1,068.60