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	$225.58	12.677%	$254.1768	$254.18	$254.20	$254.20
Purchase #2	$241.31	11.843%	$269.8883	$269.89	$269.90	$269.90
Purchase #3	$197.93	3.333%	$204.527	$204.53	$204.55	$204.50
Purchase #4	$100.42	3.808%	$104.244	$104.24	$104.25	$104.20
Purchase #5	$215.28	13.154%	$243.5979	$243.60	$243.60	$243.60
Purchase #6	$166.58	4.376%	$173.8695	$173.87	$173.85	$173.90
Purchase #7	$167.69	6.613%	$178.7793	$178.78	$178.80	$178.80
7 purchase totals =	$1,314.79		$1,429.0828	$1,429.09	$1,429.15	$1,429.10