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 $210.35   12.477%   $236.5954   $236.60   $236.60   $236.60  
  Purchase #2 $51.71   8.844%   $56.2832   $56.28   $56.30   $56.30  
  Purchase #3 $215.83   4.797%   $226.1834   $226.18   $226.20   $226.20  
  Purchase #4 $95.71   6.375%   $101.8115   $101.81   $101.80   $101.80  
  Purchase #5 $116.81   12.236%   $131.1029   $131.10   $131.10   $131.10  
  Purchase #6 $203.25   11.115%   $225.8412   $225.84   $225.85   $225.80  
  Purchase #7 $66.30   6.726%   $70.7593   $70.76   $70.75   $70.80  
  7 purchase totals = $959.96       $1,048.5769   $1,048.57   $1,048.60   $1,048.60