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	$244.94	5.667%	$258.8207	$258.82	$258.80	$258.80
Purchase #2	$85.77	5.256%	$90.2781	$90.28	$90.30	$90.30
Purchase #3	$172.30	6.503%	$183.5047	$183.50	$183.50	$183.50
Purchase #4	$92.82	10.450%	$102.5197	$102.52	$102.50	$102.50
Purchase #5	$195.76	6.413%	$208.3141	$208.31	$208.30	$208.30
Purchase #6	$128.61	12.361%	$144.5075	$144.51	$144.50	$144.50
Purchase #7	$186.37	6.192%	$197.91	$197.91	$197.90	$197.90
7 purchase totals =	$1,106.57		$1,185.8548	$1,185.85	$1,185.80	$1,185.80