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 $81.95   6.539%   $87.3087   $87.31   $87.30   $87.30  
  Purchase #2 $89.62   7.873%   $96.6758   $96.68   $96.70   $96.70  
  Purchase #3 $142.97   13.749%   $162.6269   $162.63   $162.65   $162.60  
  Purchase #4 $47.81   4.314%   $49.8725   $49.87   $49.85   $49.90  
  Purchase #5 $83.59   12.459%   $94.0045   $94.00   $94.00   $94.00  
  Purchase #6 $194.53   3.469%   $201.2782   $201.28   $201.30   $201.30  
  Purchase #7 $201.34   11.559%   $224.6129   $224.61   $224.60   $224.60  
  7 purchase totals = $841.81       $916.3795   $916.38   $916.40   $916.40