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	$29.88	11.592%	$33.3437	$33.34	$33.35	$33.30
Purchase #2	$70.60	12.821%	$79.6516	$79.65	$79.65	$79.70
Purchase #3	$104.87	5.828%	$110.9818	$110.98	$111.00	$111.00
Purchase #4	$53.58	11.825%	$59.9158	$59.92	$59.90	$59.90
Purchase #5	$88.70	12.327%	$99.634	$99.63	$99.65	$99.60
Purchase #6	$204.89	9.574%	$224.5062	$224.51	$224.50	$224.50
Purchase #7	$227.31	3.832%	$236.0205	$236.02	$236.00	$236.00
7 purchase totals =	$779.83		$844.0536	$844.05	$844.05	$844.00