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 $102.92   8.467%   $111.6342   $111.63   $111.65   $111.60  
  Purchase #2 $70.39   4.262%   $73.39   $73.39   $73.40   $73.40  
  Purchase #3 $194.28   11.786%   $217.1778   $217.18   $217.20   $217.20  
  Purchase #4 $111.55   11.486%   $124.3626   $124.36   $124.35   $124.40  
  Purchase #5 $70.49   13.170%   $79.7735   $79.77   $79.75   $79.80  
  Purchase #6 $181.93   11.295%   $202.479   $202.48   $202.50   $202.50  
  Purchase #7 $130.48   9.149%   $142.4176   $142.42   $142.40   $142.40  
  7 purchase totals = $862.04       $951.2347   $951.23   $951.25   $951.30