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	$19.42	12.532%	$21.8537	$21.85	$21.85	$21.90
Purchase #2	$162.87	10.597%	$180.1293	$180.13	$180.15	$180.10
Purchase #3	$10.95	12.298%	$12.2966	$12.30	$12.30	$12.30
Purchase #4	$191.33	10.444%	$211.3125	$211.31	$211.30	$211.30
Purchase #5	$199.30	9.684%	$218.6002	$218.60	$218.60	$218.60
Purchase #6	$208.49	4.634%	$218.1514	$218.15	$218.15	$218.20
Purchase #7	$132.83	11.338%	$147.8903	$147.89	$147.90	$147.90
7 purchase totals =	$925.19		$1,010.2340	$1,010.23	$1,010.25	$1,010.30