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	$92.86	12.304%	$104.2855	$104.29	$104.30	$104.30
Purchase #2	$143.62	9.289%	$156.9609	$156.96	$156.95	$157.00
Purchase #3	$69.86	12.722%	$78.7476	$78.75	$78.75	$78.70
Purchase #4	$20.27	6.396%	$21.5665	$21.57	$21.55	$21.60
Purchase #5	$67.77	4.251%	$70.6509	$70.65	$70.65	$70.70
Purchase #6	$91.74	7.184%	$98.3306	$98.33	$98.35	$98.30
Purchase #7	$59.40	4.102%	$61.8366	$61.84	$61.85	$61.80
7 purchase totals =	$545.52		$592.3786	$592.39	$592.40	$592.40