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	$83.78	7.719%	$90.247	$90.25	$90.25	$90.20
Purchase #2	$202.42	12.427%	$227.5747	$227.57	$227.55	$227.60
Purchase #3	$199.47	9.637%	$218.6929	$218.69	$218.70	$218.70
Purchase #4	$173.61	4.472%	$181.3738	$181.37	$181.35	$181.40
Purchase #5	$142.91	10.580%	$158.0299	$158.03	$158.05	$158.00
Purchase #6	$118.38	4.819%	$124.0847	$124.08	$124.10	$124.10
Purchase #7	$152.63	6.702%	$162.8593	$162.86	$162.85	$162.90
7 purchase totals =	$1,073.20		$1,162.8623	$1,162.85	$1,162.85	$1,162.90