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	$240.65	13.826%	$273.9223	$273.92	$273.90	$273.90
Purchase #2	$38.69	3.753%	$40.142	$40.14	$40.15	$40.10
Purchase #3	$173.43	7.514%	$186.4615	$186.46	$186.45	$186.50
Purchase #4	$149.86	5.764%	$158.4979	$158.50	$158.50	$158.50
Purchase #5	$47.30	9.364%	$51.7292	$51.73	$51.75	$51.70
Purchase #6	$169.58	10.788%	$187.8743	$187.87	$187.85	$187.90
Purchase #7	$15.90	9.517%	$17.4132	$17.41	$17.40	$17.40
7 purchase totals =	$835.41		$916.0404	$916.03	$916.00	$916.00