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	$169.50	12.185%	$190.1536	$190.15	$190.15	$190.20
Purchase #2	$18.25	11.214%	$20.2966	$20.30	$20.30	$20.30
Purchase #3	$96.38	8.269%	$104.3497	$104.35	$104.35	$104.30
Purchase #4	$8.42	8.530%	$9.1382	$9.14	$9.15	$9.10
Purchase #5	$33.81	11.429%	$37.6741	$37.67	$37.65	$37.70
Purchase #6	$239.71	10.527%	$264.9443	$264.94	$264.95	$264.90
Purchase #7	$38.36	4.720%	$40.1706	$40.17	$40.15	$40.20
7 purchase totals =	$604.43		$666.7271	$666.72	$666.70	$666.70