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	$82.42	10.365%	$90.9628	$90.96	$90.95	$91.00
Purchase #2	$207.77	12.833%	$234.4331	$234.43	$234.45	$234.40
Purchase #3	$173.46	10.105%	$190.9881	$190.99	$191.00	$191.00
Purchase #4	$242.95	5.777%	$256.9852	$256.99	$257.00	$257.00
Purchase #5	$161.93	6.286%	$172.1089	$172.11	$172.10	$172.10
Purchase #6	$174.79	3.621%	$181.1191	$181.12	$181.10	$181.10
Purchase #7	$85.32	5.410%	$89.9358	$89.94	$89.95	$89.90
7 purchase totals =	$1,128.64		$1,216.5330	$1,216.54	$1,216.55	$1,216.50