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	$149.97	3.553%	$155.2984	$155.30	$155.30	$155.30
Purchase #2	$130.42	5.685%	$137.8344	$137.83	$137.85	$137.80
Purchase #3	$165.99	3.635%	$172.0237	$172.02	$172.00	$172.00
Purchase #4	$25.79	10.337%	$28.4559	$28.46	$28.45	$28.50
Purchase #5	$219.84	8.685%	$238.9331	$238.93	$238.95	$238.90
Purchase #6	$167.86	12.571%	$188.9617	$188.96	$188.95	$189.00
Purchase #7	$47.64	12.485%	$53.5879	$53.59	$53.60	$53.60
7 purchase totals =	$907.51		$975.0951	$975.09	$975.10	$975.10