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	$234.80	4.401%	$245.1335	$245.13	$245.15	$245.10
Purchase #2	$44.90	12.354%	$50.4469	$50.45	$50.45	$50.40
Purchase #3	$232.75	9.749%	$255.4408	$255.44	$255.45	$255.40
Purchase #4	$142.70	8.846%	$155.3232	$155.32	$155.30	$155.30
Purchase #5	$92.71	4.797%	$97.1573	$97.16	$97.15	$97.20
Purchase #6	$5.82	5.676%	$6.1503	$6.15	$6.15	$6.20
Purchase #7	$99.50	11.823%	$111.2639	$111.26	$111.25	$111.30
7 purchase totals =	$853.18		$920.9159	$920.91	$920.90	$920.90