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	$138.54	3.444%	$143.3113	$143.31	$143.30	$143.30
Purchase #2	$84.55	6.347%	$89.9164	$89.92	$89.90	$89.90
Purchase #3	$129.69	13.593%	$147.3188	$147.32	$147.30	$147.30
Purchase #4	$153.48	7.701%	$165.2995	$165.30	$165.30	$165.30
Purchase #5	$151.75	9.508%	$166.1784	$166.18	$166.20	$166.20
Purchase #6	$199.77	13.105%	$225.9499	$225.95	$225.95	$225.90
Purchase #7	$86.27	4.845%	$90.4498	$90.45	$90.45	$90.40
7 purchase totals =	$944.05		$1,028.4241	$1,028.43	$1,028.40	$1,028.30