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	$159.45	6.820%	$170.3245	$170.32	$170.30	$170.30
Purchase #2	$77.72	7.663%	$83.6757	$83.68	$83.70	$83.70
Purchase #3	$241.58	9.489%	$264.5035	$264.50	$264.50	$264.50
Purchase #4	$79.34	4.555%	$82.9539	$82.95	$82.95	$83.00
Purchase #5	$183.95	11.852%	$205.7518	$205.75	$205.75	$205.80
Purchase #6	$176.26	3.208%	$181.9144	$181.91	$181.90	$181.90
Purchase #7	$12.74	9.426%	$13.9409	$13.94	$13.95	$13.90
7 purchase totals =	$931.04		$1,003.0647	$1,003.05	$1,003.05	$1,003.10