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	$246.32	13.722%	$280.12	$280.12	$280.10	$280.10
Purchase #2	$98.32	7.114%	$105.3145	$105.31	$105.30	$105.30
Purchase #3	$179.32	8.635%	$194.8043	$194.80	$194.80	$194.80
Purchase #4	$160.43	7.760%	$172.8794	$172.88	$172.90	$172.90
Purchase #5	$227.69	3.131%	$234.819	$234.82	$234.80	$234.80
Purchase #6	$230.96	13.744%	$262.7031	$262.70	$262.70	$262.70
Purchase #7	$21.35	13.790%	$24.2942	$24.29	$24.30	$24.30
7 purchase totals =	$1,164.39		$1,274.9345	$1,274.92	$1,274.90	$1,274.90