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	$16.75	9.354%	$18.3168	$18.32	$18.30	$18.30
Purchase #2	$99.92	11.779%	$111.6896	$111.69	$111.70	$111.70
Purchase #3	$86.83	4.700%	$90.911	$90.91	$90.90	$90.90
Purchase #4	$10.72	12.530%	$12.0632	$12.06	$12.05	$12.10
Purchase #5	$176.41	8.372%	$191.179	$191.18	$191.20	$191.20
Purchase #6	$42.48	6.832%	$45.3822	$45.38	$45.40	$45.40
Purchase #7	$48.58	9.118%	$53.0095	$53.01	$53.00	$53.00
7 purchase totals =	$481.69		$522.5513	$522.55	$522.55	$522.60