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 $218.48   12.593%   $245.9932   $245.99   $246.00   $246.00  
  Purchase #2 $189.59   3.694%   $196.5935   $196.59   $196.60   $196.60  
  Purchase #3 $40.60   10.712%   $44.9491   $44.95   $44.95   $44.90  
  Purchase #4 $196.35   7.387%   $210.8544   $210.85   $210.85   $210.90  
  Purchase #5 $9.88   10.409%   $10.9084   $10.91   $10.90   $10.90  
  Purchase #6 $243.44   4.182%   $253.6207   $253.62   $253.60   $253.60  
  Purchase #7 $170.60   12.565%   $192.0359   $192.04   $192.05   $192.00  
  7 purchase totals = $1,068.94       $1,154.9552   $1,154.95   $1,154.95   $1,154.90