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	$181.47	6.371%	$193.0315	$193.03	$193.05	$193.00
Purchase #2	$212.90	11.608%	$237.6134	$237.61	$237.60	$237.60
Purchase #3	$165.82	13.677%	$188.4992	$188.50	$188.50	$188.50
Purchase #4	$134.45	3.638%	$139.3413	$139.34	$139.35	$139.30
Purchase #5	$71.72	8.767%	$78.0077	$78.01	$78.00	$78.00
Purchase #6	$99.25	5.721%	$104.9281	$104.93	$104.95	$104.90
Purchase #7	$120.75	5.614%	$127.5289	$127.53	$127.55	$127.50
7 purchase totals =	$986.36		$1,068.9501	$1,068.95	$1,069.00	$1,068.80