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	$81.46	9.743%	$89.3966	$89.40	$89.40	$89.40
Purchase #2	$155.86	7.605%	$167.7132	$167.71	$167.70	$167.70
Purchase #3	$50.68	7.631%	$54.5474	$54.55	$54.55	$54.50
Purchase #4	$129.65	10.389%	$143.1193	$143.12	$143.10	$143.10
Purchase #5	$121.27	6.669%	$129.3575	$129.36	$129.35	$129.40
Purchase #6	$193.33	11.340%	$215.2536	$215.25	$215.25	$215.30
Purchase #7	$158.92	9.792%	$174.4814	$174.48	$174.50	$174.50
7 purchase totals =	$891.17		$973.8690	$973.87	$973.85	$973.90