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 $86.81   8.322%   $94.0343   $94.03   $94.05   $94.00  
  Purchase #2 $74.86   11.603%   $83.546   $83.55   $83.55   $83.50  
  Purchase #3 $88.36   11.728%   $98.7229   $98.72   $98.70   $98.70  
  Purchase #4 $48.61   3.805%   $50.4596   $50.46   $50.45   $50.50  
  Purchase #5 $32.61   11.242%   $36.276   $36.28   $36.30   $36.30  
  Purchase #6 $226.97   5.432%   $239.299   $239.30   $239.30   $239.30  
  Purchase #7 $56.78   3.671%   $58.8644   $58.86   $58.85   $58.90  
  7 purchase totals = $615.00       $661.2022   $661.20   $661.20   $661.20