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 $91.38   5.756%   $96.6398   $96.64   $96.65   $96.60  
  Purchase #2 $61.97   8.441%   $67.2009   $67.20   $67.20   $67.20  
  Purchase #3 $86.88   11.441%   $96.8199   $96.82   $96.80   $96.80  
  Purchase #4 $164.44   8.733%   $178.8005   $178.80   $178.80   $178.80  
  Purchase #5 $56.65   6.755%   $60.4767   $60.48   $60.50   $60.50  
  Purchase #6 $90.56   7.573%   $97.4181   $97.42   $97.40   $97.40  
  Purchase #7 $160.60   8.827%   $174.7762   $174.78   $174.80   $174.80  
  7 purchase totals = $712.48       $772.1321   $772.14   $772.15   $772.10