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	$93.54	10.435%	$103.3009	$103.30	$103.30	$103.30
Purchase #2	$187.97	4.188%	$195.8422	$195.84	$195.85	$195.80
Purchase #3	$96.27	6.341%	$102.3745	$102.37	$102.35	$102.40
Purchase #4	$50.70	5.439%	$53.4576	$53.46	$53.45	$53.50
Purchase #5	$114.72	10.847%	$127.1637	$127.16	$127.15	$127.20
Purchase #6	$186.83	5.817%	$197.6979	$197.70	$197.70	$197.70
Purchase #7	$38.89	4.782%	$40.7497	$40.75	$40.75	$40.70
7 purchase totals =	$768.92		$820.5865	$820.58	$820.55	$820.60