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	$235.85	8.627%	$256.1968	$256.20	$256.20	$256.20
Purchase #2	$69.41	10.244%	$76.5204	$76.52	$76.50	$76.50
Purchase #3	$223.88	8.267%	$242.3882	$242.39	$242.40	$242.40
Purchase #4	$62.51	7.573%	$67.2439	$67.24	$67.25	$67.20
Purchase #5	$40.28	12.482%	$45.3077	$45.31	$45.30	$45.30
Purchase #6	$23.69	8.507%	$25.7053	$25.71	$25.70	$25.70
Purchase #7	$37.97	5.688%	$40.1297	$40.13	$40.15	$40.10
7 purchase totals =	$693.59		$753.4920	$753.50	$753.50	$753.40