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 $57.27   8.134%   $61.9283   $61.93   $61.95   $61.90  
  Purchase #2 $197.61   8.197%   $213.8081   $213.81   $213.80   $213.80  
  Purchase #3 $169.25   11.201%   $188.2077   $188.21   $188.20   $188.20  
  Purchase #4 $164.63   4.213%   $171.5659   $171.57   $171.55   $171.60  
  Purchase #5 $95.53   13.658%   $108.5775   $108.58   $108.60   $108.60  
  Purchase #6 $13.63   13.669%   $15.4931   $15.49   $15.50   $15.50  
  Purchase #7 $224.81   3.404%   $232.4625   $232.46   $232.45   $232.50  
  7 purchase totals = $922.73       $992.0431   $992.05   $992.05   $992.10