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 $96.44   10.497%   $106.5633   $106.56   $106.55   $106.60  
  Purchase #2 $74.90   8.623%   $81.3586   $81.36   $81.35   $81.40  
  Purchase #3 $38.45   11.677%   $42.9398   $42.94   $42.95   $42.90  
  Purchase #4 $212.84   6.454%   $226.5767   $226.58   $226.60   $226.60  
  Purchase #5 $192.73   8.828%   $209.7442   $209.74   $209.75   $209.70  
  Purchase #6 $41.43   11.464%   $46.1795   $46.18   $46.20   $46.20  
  Purchase #7 $127.94   11.359%   $142.4727   $142.47   $142.45   $142.50  
  7 purchase totals = $784.73       $855.8348   $855.83   $855.85   $855.90