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	$170.42	11.411%	$189.8666	$189.87	$189.85	$189.90
Purchase #2	$33.33	3.828%	$34.6059	$34.61	$34.60	$34.60
Purchase #3	$50.80	13.711%	$57.7652	$57.77	$57.75	$57.80
Purchase #4	$211.29	11.528%	$235.6475	$235.65	$235.65	$235.60
Purchase #5	$218.30	5.823%	$231.0116	$231.01	$231.00	$231.00
Purchase #6	$234.72	7.127%	$251.4485	$251.45	$251.45	$251.40
Purchase #7	$52.44	13.377%	$59.4549	$59.45	$59.45	$59.50
7 purchase totals =	$971.30		$1,059.8002	$1,059.81	$1,059.75	$1,059.80