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 $61.82   6.462%   $65.8148   $65.81   $65.80   $65.80  
  Purchase #2 $202.87   7.537%   $218.1603   $218.16   $218.15   $218.20  
  Purchase #3 $248.99   9.720%   $273.1918   $273.19   $273.20   $273.20  
  Purchase #4 $176.44   3.563%   $182.7266   $182.73   $182.75   $182.70  
  Purchase #5 $28.29   8.374%   $30.659   $30.66   $30.65   $30.70  
  Purchase #6 $243.69   13.602%   $276.8367   $276.84   $276.85   $276.80  
  Purchase #7 $14.68   10.335%   $16.1972   $16.20   $16.20   $16.20  
  7 purchase totals = $976.78       $1,063.5864   $1,063.59   $1,063.60   $1,063.60