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	$150.75	13.648%	$171.3244	$171.32	$171.30	$171.30
Purchase #2	$175.48	13.805%	$199.705	$199.71	$199.70	$199.70
Purchase #3	$122.60	8.158%	$132.6017	$132.60	$132.60	$132.60
Purchase #4	$105.91	5.498%	$111.7329	$111.73	$111.75	$111.70
Purchase #5	$195.68	10.789%	$216.7919	$216.79	$216.80	$216.80
Purchase #6	$160.58	4.219%	$167.3549	$167.35	$167.35	$167.40
Purchase #7	$45.95	11.293%	$51.1391	$51.14	$51.15	$51.10
7 purchase totals =	$956.95		$1,050.6499	$1,050.64	$1,050.65	$1,050.60