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	$38.50	9.491%	$42.154	$42.15	$42.15	$42.20
Purchase #2	$34.41	10.834%	$38.138	$38.14	$38.15	$38.10
Purchase #3	$19.54	11.234%	$21.7351	$21.74	$21.75	$21.70
Purchase #4	$131.66	7.570%	$141.6267	$141.63	$141.65	$141.60
Purchase #5	$62.99	13.232%	$71.3248	$71.32	$71.30	$71.30
Purchase #6	$156.29	11.287%	$173.9305	$173.93	$173.95	$173.90
Purchase #7	$215.93	12.559%	$243.0486	$243.05	$243.05	$243.00
7 purchase totals =	$659.32		$731.9577	$731.96	$732.00	$731.80