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	$165.41	9.523%	$181.162	$181.16	$181.15	$181.20
Purchase #2	$245.97	4.725%	$257.5921	$257.59	$257.60	$257.60
Purchase #3	$137.81	5.329%	$145.1539	$145.15	$145.15	$145.20
Purchase #4	$238.90	12.297%	$268.2775	$268.28	$268.30	$268.30
Purchase #5	$34.78	7.361%	$37.3402	$37.34	$37.35	$37.30
Purchase #6	$157.59	5.550%	$166.3362	$166.34	$166.35	$166.30
Purchase #7	$9.66	6.459%	$10.2839	$10.28	$10.30	$10.30
7 purchase totals =	$990.12		$1,066.1458	$1,066.14	$1,066.20	$1,066.20