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	$46.49	9.474%	$50.8945	$50.89	$50.90	$50.90
Purchase #2	$207.98	6.653%	$221.8169	$221.82	$221.80	$221.80
Purchase #3	$56.90	13.557%	$64.6139	$64.61	$64.60	$64.60
Purchase #4	$89.41	5.322%	$94.1684	$94.17	$94.15	$94.20
Purchase #5	$228.30	7.429%	$245.2604	$245.26	$245.25	$245.30
Purchase #6	$145.85	3.446%	$150.876	$150.88	$150.90	$150.90
Purchase #7	$50.98	5.342%	$53.7034	$53.70	$53.70	$53.70
7 purchase totals =	$825.91		$881.3335	$881.33	$881.30	$881.40