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 $119.43   3.540%   $123.6578   $123.66   $123.65   $123.70  
  Purchase #2 $69.97   4.465%   $73.0942   $73.09   $73.10   $73.10  
  Purchase #3 $75.74   8.246%   $81.9855   $81.99   $82.00   $82.00  
  Purchase #4 $48.76   6.565%   $51.9611   $51.96   $51.95   $52.00  
  Purchase #5 $210.96   4.827%   $221.143   $221.14   $221.15   $221.10  
  Purchase #6 $97.64   4.151%   $101.693   $101.69   $101.70   $101.70  
  Purchase #7 $214.51   9.569%   $235.0365   $235.04   $235.05   $235.00  
  7 purchase totals = $837.01       $888.5711   $888.57   $888.60   $888.60