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	$106.27	13.640%	$120.7652	$120.77	$120.75	$120.80
Purchase #2	$199.59	11.377%	$222.2974	$222.30	$222.30	$222.30
Purchase #3	$90.64	7.374%	$97.3238	$97.32	$97.30	$97.30
Purchase #4	$108.49	6.281%	$115.3043	$115.30	$115.30	$115.30
Purchase #5	$34.94	12.760%	$39.3983	$39.40	$39.40	$39.40
Purchase #6	$104.37	6.428%	$111.0789	$111.08	$111.10	$111.10
Purchase #7	$147.71	5.249%	$155.4633	$155.46	$155.45	$155.50
7 purchase totals =	$792.01		$861.6312	$861.63	$861.60	$861.70