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	$89.75	11.551%	$100.117	$100.12	$100.10	$100.10
Purchase #2	$138.82	3.321%	$143.4302	$143.43	$143.45	$143.40
Purchase #3	$154.57	11.865%	$172.9097	$172.91	$172.90	$172.90
Purchase #4	$82.36	3.639%	$85.3571	$85.36	$85.35	$85.40
Purchase #5	$248.99	3.613%	$257.986	$257.99	$258.00	$258.00
Purchase #6	$122.91	9.783%	$134.9343	$134.93	$134.95	$134.90
Purchase #7	$202.38	10.222%	$223.0673	$223.07	$223.05	$223.10
7 purchase totals =	$1,039.78		$1,117.8016	$1,117.81	$1,117.80	$1,117.80