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	$82.69	9.692%	$90.7043	$90.70	$90.70	$90.70
Purchase #2	$230.69	13.361%	$261.5125	$261.51	$261.50	$261.50
Purchase #3	$165.50	6.830%	$176.8037	$176.80	$176.80	$176.80
Purchase #4	$50.53	7.510%	$54.3248	$54.32	$54.30	$54.30
Purchase #5	$172.91	13.483%	$196.2235	$196.22	$196.20	$196.20
Purchase #6	$105.26	6.258%	$111.8472	$111.85	$111.85	$111.80
Purchase #7	$116.93	8.495%	$126.8632	$126.86	$126.85	$126.90
7 purchase totals =	$924.51		$1,018.2792	$1,018.26	$1,018.20	$1,018.20