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	$78.85	7.172%	$84.5051	$84.51	$84.50	$84.50
Purchase #2	$167.79	4.740%	$175.7432	$175.74	$175.75	$175.70
Purchase #3	$58.71	6.664%	$62.6224	$62.62	$62.60	$62.60
Purchase #4	$110.62	11.784%	$123.6555	$123.66	$123.65	$123.70
Purchase #5	$177.30	4.545%	$185.3583	$185.36	$185.35	$185.40
Purchase #6	$115.78	13.104%	$130.9518	$130.95	$130.95	$131.00
Purchase #7	$29.59	12.449%	$33.2737	$33.27	$33.25	$33.30
7 purchase totals =	$738.64		$796.1100	$796.11	$796.05	$796.20