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 $88.46   9.278%   $96.6673   $96.67   $96.65   $96.70  
  Purchase #2 $71.59   11.176%   $79.5909   $79.59   $79.60   $79.60  
  Purchase #3 $92.53   5.244%   $97.3823   $97.38   $97.40   $97.40  
  Purchase #4 $105.66   13.141%   $119.5448   $119.54   $119.55   $119.50  
  Purchase #5 $65.70   4.535%   $68.6795   $68.68   $68.70   $68.70  
  Purchase #6 $219.47   6.150%   $232.9674   $232.97   $232.95   $233.00  
  Purchase #7 $213.66   11.803%   $238.8783   $238.88   $238.90   $238.90  
  7 purchase totals = $857.07       $933.7105   $933.71   $933.75   $933.80