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	$30.72	3.435%	$31.7752	$31.78	$31.80	$31.80
Purchase #2	$184.44	7.374%	$198.0406	$198.04	$198.05	$198.00
Purchase #3	$140.77	12.692%	$158.6365	$158.64	$158.65	$158.60
Purchase #4	$49.65	10.451%	$54.8389	$54.84	$54.85	$54.80
Purchase #5	$147.76	9.742%	$162.1548	$162.15	$162.15	$162.20
Purchase #6	$59.51	10.643%	$65.8436	$65.84	$65.85	$65.80
Purchase #7	$183.59	8.558%	$199.3016	$199.30	$199.30	$199.30
7 purchase totals =	$796.44		$870.5912	$870.59	$870.65	$870.50