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	$227.33	5.583%	$240.0218	$240.02	$240.00	$240.00
Purchase #2	$82.76	8.331%	$89.6547	$89.65	$89.65	$89.70
Purchase #3	$81.99	3.847%	$85.1442	$85.14	$85.15	$85.10
Purchase #4	$54.93	12.140%	$61.5985	$61.60	$61.60	$61.60
Purchase #5	$59.71	9.417%	$65.3329	$65.33	$65.35	$65.30
Purchase #6	$17.59	12.544%	$19.7965	$19.80	$19.80	$19.80
Purchase #7	$94.71	6.633%	$100.9921	$100.99	$101.00	$101.00
7 purchase totals =	$619.02		$662.5407	$662.53	$662.55	$662.50