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 $195.71   13.381%   $221.898   $221.90   $221.90   $221.90  
  Purchase #2 $66.77   10.489%   $73.7735   $73.77   $73.75   $73.80  
  Purchase #3 $53.38   4.481%   $55.772   $55.77   $55.75   $55.80  
  Purchase #4 $226.68   11.120%   $251.8868   $251.89   $251.90   $251.90  
  Purchase #5 $217.94   8.163%   $235.7304   $235.73   $235.75   $235.70  
  Purchase #6 $5.96   13.822%   $6.7838   $6.78   $6.80   $6.80  
  Purchase #7 $176.75   3.586%   $183.0883   $183.09   $183.10   $183.10  
  7 purchase totals = $943.19       $1,028.9328   $1,028.93   $1,028.95   $1,029.00