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	$13.53	12.643%	$15.2406	$15.24	$15.25	$15.20
Purchase #2	$114.44	11.631%	$127.7505	$127.75	$127.75	$127.80
Purchase #3	$41.33	13.132%	$46.7575	$46.76	$46.75	$46.80
Purchase #4	$105.54	10.211%	$116.3167	$116.32	$116.30	$116.30
Purchase #5	$208.64	7.371%	$224.0189	$224.02	$224.00	$224.00
Purchase #6	$230.27	4.350%	$240.2867	$240.29	$240.30	$240.30
Purchase #7	$75.88	12.753%	$85.557	$85.56	$85.55	$85.60
7 purchase totals =	$789.63		$855.9279	$855.94	$855.90	$856.00