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	$149.99	8.280%	$162.4092	$162.41	$162.40	$162.40
Purchase #2	$73.74	7.251%	$79.0869	$79.09	$79.10	$79.10
Purchase #3	$249.32	5.657%	$263.424	$263.42	$263.40	$263.40
Purchase #4	$74.60	5.334%	$78.5792	$78.58	$78.60	$78.60
Purchase #5	$250.95	11.420%	$279.6085	$279.61	$279.60	$279.60
Purchase #6	$33.27	12.782%	$37.5226	$37.52	$37.50	$37.50
Purchase #7	$47.42	5.699%	$50.1225	$50.12	$50.10	$50.10
7 purchase totals =	$879.29		$950.7529	$950.75	$950.70	$950.70