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	$112.65	3.540%	$116.6378	$116.64	$116.65	$116.60
Purchase #2	$99.91	3.752%	$103.6586	$103.66	$103.65	$103.70
Purchase #3	$104.66	6.594%	$111.5613	$111.56	$111.55	$111.60
Purchase #4	$161.46	12.808%	$182.1398	$182.14	$182.15	$182.10
Purchase #5	$48.26	11.403%	$53.7631	$53.76	$53.75	$53.80
Purchase #6	$123.26	10.450%	$136.1407	$136.14	$136.15	$136.10
Purchase #7	$76.67	4.240%	$79.9208	$79.92	$79.90	$79.90
7 purchase totals =	$726.87		$783.8221	$783.82	$783.80	$783.80