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	$85.90	5.524%	$90.6451	$90.65	$90.65	$90.60
Purchase #2	$77.58	10.487%	$85.7158	$85.72	$85.70	$85.70
Purchase #3	$60.86	8.729%	$66.1725	$66.17	$66.15	$66.20
Purchase #4	$58.26	3.598%	$60.3562	$60.36	$60.35	$60.40
Purchase #5	$90.74	6.232%	$96.3949	$96.39	$96.40	$96.40
Purchase #6	$101.58	11.372%	$113.1317	$113.13	$113.15	$113.10
Purchase #7	$71.77	13.482%	$81.446	$81.45	$81.45	$81.40
7 purchase totals =	$546.69		$593.8622	$593.87	$593.85	$593.80