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 $93.83   10.782%   $103.9468   $103.95   $103.95   $103.90  
  Purchase #2 $56.37   10.679%   $62.3898   $62.39   $62.40   $62.40  
  Purchase #3 $177.91   6.688%   $189.8086   $189.81   $189.80   $189.80  
  Purchase #4 $90.91   7.468%   $97.6992   $97.70   $97.70   $97.70  
  Purchase #5 $175.92   6.451%   $187.2686   $187.27   $187.25   $187.30  
  Purchase #6 $233.41   13.436%   $264.771   $264.77   $264.75   $264.80  
  Purchase #7 $47.67   6.556%   $50.7952   $50.80   $50.80   $50.80  
  7 purchase totals = $876.02       $956.6792   $956.69   $956.65   $956.70