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	$172.90	3.715%	$179.3232	$179.32	$179.30	$179.30
Purchase #2	$55.36	10.525%	$61.1866	$61.19	$61.20	$61.20
Purchase #3	$36.30	8.732%	$39.4697	$39.47	$39.45	$39.50
Purchase #4	$85.42	3.870%	$88.7258	$88.73	$88.75	$88.70
Purchase #5	$188.83	10.553%	$208.7572	$208.76	$208.75	$208.80
Purchase #6	$132.27	13.741%	$150.4452	$150.45	$150.45	$150.40
Purchase #7	$58.26	4.476%	$60.8677	$60.87	$60.85	$60.90
7 purchase totals =	$729.34		$788.7754	$788.79	$788.75	$788.80