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	$250.60	9.788%	$275.1287	$275.13	$275.15	$275.10
Purchase #2	$89.54	13.755%	$101.8562	$101.86	$101.85	$101.90
Purchase #3	$14.47	7.676%	$15.5807	$15.58	$15.60	$15.60
Purchase #4	$233.33	7.146%	$250.0038	$250.00	$250.00	$250.00
Purchase #5	$157.48	10.432%	$173.9083	$173.91	$173.90	$173.90
Purchase #6	$249.31	6.862%	$266.4177	$266.42	$266.40	$266.40
Purchase #7	$6.30	7.500%	$6.7725	$6.77	$6.75	$6.80
7 purchase totals =	$1,001.03		$1,089.6679	$1,089.67	$1,089.65	$1,089.70