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	$159.83	5.488%	$168.6015	$168.60	$168.60	$168.60
Purchase #2	$210.92	12.223%	$236.7008	$236.70	$236.70	$236.70
Purchase #3	$170.78	12.701%	$192.4708	$192.47	$192.45	$192.50
Purchase #4	$79.35	12.162%	$89.0005	$89.00	$89.00	$89.00
Purchase #5	$192.38	8.328%	$208.4014	$208.40	$208.40	$208.40
Purchase #6	$133.30	7.590%	$143.4175	$143.42	$143.40	$143.40
Purchase #7	$174.69	6.391%	$185.8544	$185.85	$185.85	$185.90
7 purchase totals =	$1,121.25		$1,224.4469	$1,224.44	$1,224.40	$1,224.50