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	$156.48	11.125%	$173.8884	$173.89	$173.90	$173.90
Purchase #2	$79.77	5.226%	$83.9388	$83.94	$83.95	$83.90
Purchase #3	$53.88	3.525%	$55.7793	$55.78	$55.80	$55.80
Purchase #4	$240.93	6.427%	$256.4146	$256.41	$256.40	$256.40
Purchase #5	$19.32	9.521%	$21.1595	$21.16	$21.15	$21.20
Purchase #6	$18.81	7.414%	$20.2046	$20.20	$20.20	$20.20
Purchase #7	$235.41	9.190%	$257.0442	$257.04	$257.05	$257.00
7 purchase totals =	$804.60		$868.4294	$868.42	$868.45	$868.40