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	$65.52	4.538%	$68.4933	$68.49	$68.50	$68.50
Purchase #2	$219.87	3.630%	$227.8513	$227.85	$227.85	$227.90
Purchase #3	$49.48	12.584%	$55.7066	$55.71	$55.70	$55.70
Purchase #4	$163.47	13.708%	$185.8785	$185.88	$185.90	$185.90
Purchase #5	$98.64	12.194%	$110.6682	$110.67	$110.65	$110.70
Purchase #6	$26.30	6.493%	$28.0077	$28.01	$28.00	$28.00
Purchase #7	$79.73	12.403%	$89.6189	$89.62	$89.60	$89.60
7 purchase totals =	$703.01		$766.2245	$766.23	$766.20	$766.30