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 $93.61   3.521%   $96.906   $96.91   $96.90   $96.90  
  Purchase #2 $221.59   13.257%   $250.9662   $250.97   $250.95   $251.00  
  Purchase #3 $71.55   13.367%   $81.1141   $81.11   $81.10   $81.10  
  Purchase #4 $192.82   12.195%   $216.3344   $216.33   $216.35   $216.30  
  Purchase #5 $49.66   11.218%   $55.2309   $55.23   $55.25   $55.20  
  Purchase #6 $110.77   5.138%   $116.4614   $116.46   $116.45   $116.50  
  Purchase #7 $170.72   4.738%   $178.8087   $178.81   $178.80   $178.80  
  7 purchase totals = $910.72       $995.8217   $995.82   $995.80   $995.80