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	$22.60	5.852%	$23.9226	$23.92	$23.90	$23.90
Purchase #2	$79.74	11.218%	$88.6852	$88.69	$88.70	$88.70
Purchase #3	$191.51	4.636%	$200.3884	$200.39	$200.40	$200.40
Purchase #4	$145.52	10.315%	$160.5304	$160.53	$160.55	$160.50
Purchase #5	$90.99	10.139%	$100.2155	$100.22	$100.20	$100.20
Purchase #6	$196.69	7.740%	$211.9138	$211.91	$211.90	$211.90
Purchase #7	$206.69	13.107%	$233.7809	$233.78	$233.80	$233.80
7 purchase totals =	$933.74		$1,019.4368	$1,019.44	$1,019.45	$1,019.40