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 $108.34   7.686%   $116.667   $116.67   $116.65   $116.70  
  Purchase #2 $38.44   8.537%   $41.7216   $41.72   $41.70   $41.70  
  Purchase #3 $47.25   5.295%   $49.7519   $49.75   $49.75   $49.80  
  Purchase #4 $87.83   6.315%   $93.3765   $93.38   $93.40   $93.40  
  Purchase #5 $131.38   3.474%   $135.9441   $135.94   $135.95   $135.90  
  Purchase #6 $188.93   4.740%   $197.8853   $197.89   $197.90   $197.90  
  Purchase #7 $87.97   10.654%   $97.3423   $97.34   $97.35   $97.30  
  7 purchase totals = $690.14       $732.6887   $732.69   $732.70   $732.70