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 $21.96   8.374%   $23.7989   $23.80   $23.80   $23.80  
  Purchase #2 $113.68   4.722%   $119.048   $119.05   $119.05   $119.00  
  Purchase #3 $55.60   7.124%   $59.5609   $59.56   $59.55   $59.60  
  Purchase #4 $67.53   9.106%   $73.6793   $73.68   $73.70   $73.70  
  Purchase #5 $226.76   6.447%   $241.3792   $241.38   $241.40   $241.40  
  Purchase #6 $97.71   10.821%   $108.2832   $108.28   $108.30   $108.30  
  Purchase #7 $95.54   3.534%   $98.9164   $98.92   $98.90   $98.90  
  7 purchase totals = $678.78       $724.6659   $724.67   $724.70   $724.70