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 $226.67   10.587%   $250.6676   $250.67   $250.65   $250.70  
  Purchase #2 $171.77   13.196%   $194.4368   $194.44   $194.45   $194.40  
  Purchase #3 $170.81   10.643%   $188.9893   $188.99   $189.00   $189.00  
  Purchase #4 $176.55   4.164%   $183.9015   $183.90   $183.90   $183.90  
  Purchase #5 $204.87   5.622%   $216.3878   $216.39   $216.40   $216.40  
  Purchase #6 $53.54   13.858%   $60.9596   $60.96   $60.95   $61.00  
  Purchase #7 $166.58   4.698%   $174.4059   $174.41   $174.40   $174.40  
  7 purchase totals = $1,170.79       $1,269.7485   $1,269.76   $1,269.75   $1,269.80