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	$75.87	13.110%	$85.8166	$85.82	$85.80	$85.80
Purchase #2	$136.61	13.805%	$155.469	$155.47	$155.45	$155.50
Purchase #3	$208.69	12.405%	$234.578	$234.58	$234.60	$234.60
Purchase #4	$27.65	4.814%	$28.9811	$28.98	$29.00	$29.00
Purchase #5	$115.38	12.216%	$129.4748	$129.47	$129.45	$129.50
Purchase #6	$37.60	13.384%	$42.6324	$42.63	$42.65	$42.60
Purchase #7	$244.70	10.449%	$270.2687	$270.27	$270.25	$270.30
7 purchase totals =	$846.50		$947.2206	$947.22	$947.20	$947.30