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	$36.41	10.798%	$40.3416	$40.34	$40.35	$40.30
Purchase #2	$116.68	11.455%	$130.0457	$130.05	$130.05	$130.00
Purchase #3	$152.99	3.853%	$158.8847	$158.88	$158.90	$158.90
Purchase #4	$88.50	13.641%	$100.5723	$100.57	$100.55	$100.60
Purchase #5	$200.69	7.282%	$215.3042	$215.30	$215.30	$215.30
Purchase #6	$173.79	10.194%	$191.5062	$191.51	$191.50	$191.50
Purchase #7	$56.82	7.544%	$61.1065	$61.11	$61.10	$61.10
7 purchase totals =	$825.88		$897.7612	$897.76	$897.75	$897.70