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 $69.50   6.190%   $73.8021   $73.80   $73.80   $73.80  
  Purchase #2 $249.33   5.179%   $262.2428   $262.24   $262.25   $262.20  
  Purchase #3 $168.70   12.583%   $189.9275   $189.93   $189.95   $189.90  
  Purchase #4 $70.92   8.483%   $76.9361   $76.94   $76.95   $76.90  
  Purchase #5 $110.50   13.713%   $125.6529   $125.65   $125.65   $125.70  
  Purchase #6 $130.75   11.675%   $146.0151   $146.02   $146.00   $146.00  
  Purchase #7 $35.69   12.168%   $40.0328   $40.03   $40.05   $40.00  
  7 purchase totals = $835.39       $914.6093   $914.61   $914.65   $914.50