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	$85.39	7.180%	$91.521	$91.52	$91.50	$91.50
Purchase #2	$180.75	4.515%	$188.9109	$188.91	$188.90	$188.90
Purchase #3	$56.89	3.514%	$58.8891	$58.89	$58.90	$58.90
Purchase #4	$250.87	8.518%	$272.2391	$272.24	$272.25	$272.20
Purchase #5	$99.56	9.649%	$109.1665	$109.17	$109.15	$109.20
Purchase #6	$99.89	11.176%	$111.0537	$111.05	$111.05	$111.10
Purchase #7	$236.37	7.324%	$253.6817	$253.68	$253.70	$253.70
7 purchase totals =	$1,009.72		$1,085.4620	$1,085.46	$1,085.45	$1,085.50