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	$145.91	6.296%	$155.0965	$155.10	$155.10	$155.10
Purchase #2	$127.47	9.148%	$139.131	$139.13	$139.15	$139.10
Purchase #3	$217.58	7.266%	$233.3894	$233.39	$233.40	$233.40
Purchase #4	$228.28	3.136%	$235.4389	$235.44	$235.45	$235.40
Purchase #5	$175.45	8.506%	$190.3738	$190.37	$190.35	$190.40
Purchase #6	$25.60	12.482%	$28.7954	$28.80	$28.80	$28.80
Purchase #7	$29.31	13.823%	$33.3615	$33.36	$33.35	$33.40
7 purchase totals =	$949.60		$1,015.5865	$1,015.59	$1,015.60	$1,015.60