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	$204.91	5.403%	$215.9813	$215.98	$216.00	$216.00
Purchase #2	$118.76	4.677%	$124.3144	$124.31	$124.30	$124.30
Purchase #3	$30.25	4.151%	$31.5057	$31.51	$31.50	$31.50
Purchase #4	$54.60	12.789%	$61.5828	$61.58	$61.60	$61.60
Purchase #5	$28.65	5.815%	$30.316	$30.32	$30.30	$30.30
Purchase #6	$234.66	12.337%	$263.61	$263.61	$263.60	$263.60
Purchase #7	$103.96	7.180%	$111.4243	$111.42	$111.40	$111.40
7 purchase totals =	$775.79		$838.7345	$838.73	$838.70	$838.70