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	$115.97	10.287%	$127.8998	$127.90	$127.90	$127.90
Purchase #2	$35.47	4.814%	$37.1775	$37.18	$37.20	$37.20
Purchase #3	$55.27	10.599%	$61.1281	$61.13	$61.15	$61.10
Purchase #4	$10.47	4.753%	$10.9676	$10.97	$10.95	$11.00
Purchase #5	$15.71	12.741%	$17.7116	$17.71	$17.70	$17.70
Purchase #6	$84.91	11.409%	$94.5974	$94.60	$94.60	$94.60
Purchase #7	$36.25	10.411%	$40.024	$40.02	$40.00	$40.00
7 purchase totals =	$354.05		$389.5060	$389.51	$389.50	$389.50