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 $53.90   13.505%   $61.1792   $61.18   $61.20   $61.20  
  Purchase #2 $73.36   8.200%   $79.3755   $79.38   $79.40   $79.40  
  Purchase #3 $115.79   3.372%   $119.6944   $119.69   $119.70   $119.70  
  Purchase #4 $106.28   8.664%   $115.4881   $115.49   $115.50   $115.50  
  Purchase #5 $201.63   4.808%   $211.3244   $211.32   $211.30   $211.30  
  Purchase #6 $168.65   12.431%   $189.6149   $189.61   $189.60   $189.60  
  Purchase #7 $82.85   11.440%   $92.328   $92.33   $92.35   $92.30  
  7 purchase totals = $802.46       $869.0045   $869.00   $869.05   $869.00