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	$240.70	12.777%	$271.4542	$271.45	$271.45	$271.50
Purchase #2	$162.80	13.467%	$184.7243	$184.72	$184.70	$184.70
Purchase #3	$76.34	4.221%	$79.5623	$79.56	$79.55	$79.60
Purchase #4	$110.71	11.342%	$123.2667	$123.27	$123.25	$123.30
Purchase #5	$136.35	10.867%	$151.1672	$151.17	$151.15	$151.20
Purchase #6	$75.45	9.827%	$82.8645	$82.86	$82.85	$82.90
Purchase #7	$39.49	8.624%	$42.8956	$42.90	$42.90	$42.90
7 purchase totals =	$841.84		$935.9348	$935.93	$935.85	$936.10