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 $195.80   11.794%   $218.8927   $218.89   $218.90   $218.90  
  Purchase #2 $249.97   4.665%   $261.6311   $261.63   $261.65   $261.60  
  Purchase #3 $56.42   6.822%   $60.269   $60.27   $60.25   $60.30  
  Purchase #4 $16.55   9.141%   $18.0628   $18.06   $18.05   $18.10  
  Purchase #5 $238.58   11.505%   $266.0286   $266.03   $266.05   $266.00  
  Purchase #6 $62.35   4.109%   $64.912   $64.91   $64.90   $64.90  
  Purchase #7 $54.67   4.133%   $56.9295   $56.93   $56.95   $56.90  
  7 purchase totals = $874.34       $946.7257   $946.72   $946.75   $946.70