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	$140.91	12.426%	$158.4195	$158.42	$158.40	$158.40
Purchase #2	$205.32	11.157%	$228.2276	$228.23	$228.25	$228.20
Purchase #3	$205.41	5.621%	$216.9561	$216.96	$216.95	$217.00
Purchase #4	$35.48	4.228%	$36.9801	$36.98	$37.00	$37.00
Purchase #5	$182.63	9.707%	$200.3579	$200.36	$200.35	$200.40
Purchase #6	$215.85	5.865%	$228.5096	$228.51	$228.50	$228.50
Purchase #7	$64.42	9.405%	$70.4787	$70.48	$70.50	$70.50
7 purchase totals =	$1,050.02		$1,139.9295	$1,139.94	$1,139.95	$1,140.00