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	$221.28	13.802%	$251.8211	$251.82	$251.80	$251.80
Purchase #2	$106.36	4.863%	$111.5323	$111.53	$111.55	$111.50
Purchase #3	$210.56	5.529%	$222.2019	$222.20	$222.20	$222.20
Purchase #4	$57.85	13.805%	$65.8362	$65.84	$65.85	$65.80
Purchase #5	$205.72	11.541%	$229.4621	$229.46	$229.45	$229.50
Purchase #6	$79.65	13.237%	$90.1933	$90.19	$90.20	$90.20
Purchase #7	$53.59	6.637%	$57.1468	$57.15	$57.15	$57.10
7 purchase totals =	$935.01		$1,028.1937	$1,028.19	$1,028.20	$1,028.10