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 $84.43   13.447%   $95.7833   $95.78   $95.80   $95.80  
  Purchase #2 $174.64   8.338%   $189.2015   $189.20   $189.20   $189.20  
  Purchase #3 $246.54   10.470%   $272.3527   $272.35   $272.35   $272.40  
  Purchase #4 $50.77   10.830%   $56.2684   $56.27   $56.25   $56.30  
  Purchase #5 $91.91   6.390%   $97.783   $97.78   $97.80   $97.80  
  Purchase #6 $109.63   7.757%   $118.134   $118.13   $118.15   $118.10  
  Purchase #7 $95.96   8.674%   $104.2836   $104.28   $104.30   $104.30  
  7 purchase totals = $853.88       $933.8065   $933.79   $933.85   $933.90