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	$189.87	4.531%	$198.473	$198.47	$198.45	$198.50
Purchase #2	$144.71	11.752%	$161.7163	$161.72	$161.70	$161.70
Purchase #3	$55.83	3.780%	$57.9404	$57.94	$57.95	$57.90
Purchase #4	$106.49	5.114%	$111.9359	$111.94	$111.95	$111.90
Purchase #5	$245.64	5.378%	$258.8505	$258.85	$258.85	$258.90
Purchase #6	$135.91	11.598%	$151.6728	$151.67	$151.65	$151.70
Purchase #7	$50.82	5.359%	$53.5434	$53.54	$53.55	$53.50
7 purchase totals =	$929.27		$994.1323	$994.13	$994.10	$994.10