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	$121.30	10.544%	$134.0899	$134.09	$134.10	$134.10
Purchase #2	$157.66	9.545%	$172.7086	$172.71	$172.70	$172.70
Purchase #3	$5.46	8.350%	$5.9159	$5.92	$5.90	$5.90
Purchase #4	$47.69	11.374%	$53.1143	$53.11	$53.10	$53.10
Purchase #5	$6.82	9.820%	$7.4897	$7.49	$7.50	$7.50
Purchase #6	$109.91	13.370%	$124.605	$124.61	$124.60	$124.60
Purchase #7	$124.60	13.557%	$141.492	$141.49	$141.50	$141.50
7 purchase totals =	$573.44		$639.4154	$639.42	$639.40	$639.40