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 $206.94   5.690%   $218.7149   $218.71   $218.70   $218.70  
  Purchase #2 $241.83   10.771%   $267.8775   $267.88   $267.90   $267.90  
  Purchase #3 $26.42   8.791%   $28.7426   $28.74   $28.75   $28.70  
  Purchase #4 $25.53   3.575%   $26.4427   $26.44   $26.45   $26.40  
  Purchase #5 $44.95   12.567%   $50.5989   $50.60   $50.60   $50.60  
  Purchase #6 $250.71   10.391%   $276.7613   $276.76   $276.75   $276.80  
  Purchase #7 $225.68   9.561%   $247.2573   $247.26   $247.25   $247.30  
  7 purchase totals = $1,022.06       $1,116.3952   $1,116.39   $1,116.40   $1,116.40