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	$38.25	11.299%	$42.5719	$42.57	$42.55	$42.60
Purchase #2	$83.41	5.473%	$87.975	$87.98	$88.00	$88.00
Purchase #3	$67.91	10.653%	$75.1445	$75.14	$75.15	$75.10
Purchase #4	$138.66	9.221%	$151.4458	$151.45	$151.45	$151.40
Purchase #5	$102.30	9.146%	$111.6564	$111.66	$111.65	$111.70
Purchase #6	$55.71	5.448%	$58.7451	$58.75	$58.75	$58.70
Purchase #7	$142.32	9.795%	$156.2602	$156.26	$156.25	$156.30
7 purchase totals =	$628.56		$683.7989	$683.81	$683.80	$683.80