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	$171.82	3.675%	$178.1344	$178.13	$178.15	$178.10
Purchase #2	$186.61	11.367%	$207.822	$207.82	$207.80	$207.80
Purchase #3	$105.86	3.136%	$109.1798	$109.18	$109.20	$109.20
Purchase #4	$114.41	3.672%	$118.6111	$118.61	$118.60	$118.60
Purchase #5	$12.31	13.221%	$13.9375	$13.94	$13.95	$13.90
Purchase #6	$43.33	7.513%	$46.5854	$46.59	$46.60	$46.60
Purchase #7	$200.53	12.448%	$225.492	$225.49	$225.50	$225.50
7 purchase totals =	$834.87		$899.7622	$899.76	$899.80	$899.70