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	$109.83	9.781%	$120.5725	$120.57	$120.55	$120.60
Purchase #2	$154.85	11.428%	$172.5463	$172.55	$172.55	$172.50
Purchase #3	$73.91	13.416%	$83.8258	$83.83	$83.85	$83.80
Purchase #4	$62.48	6.668%	$66.6462	$66.65	$66.65	$66.60
Purchase #5	$58.54	5.585%	$61.8095	$61.81	$61.80	$61.80
Purchase #6	$214.41	10.149%	$236.1705	$236.17	$236.15	$236.20
Purchase #7	$123.89	7.220%	$132.8349	$132.83	$132.85	$132.80
7 purchase totals =	$797.91		$874.4057	$874.41	$874.40	$874.30