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	$29.79	8.329%	$32.2712	$32.27	$32.25	$32.30
Purchase #2	$189.66	5.169%	$199.4635	$199.46	$199.45	$199.50
Purchase #3	$37.72	8.444%	$40.9051	$40.91	$40.90	$40.90
Purchase #4	$211.78	12.463%	$238.1741	$238.17	$238.15	$238.20
Purchase #5	$234.88	9.808%	$257.917	$257.92	$257.90	$257.90
Purchase #6	$40.49	6.370%	$43.0692	$43.07	$43.05	$43.10
Purchase #7	$116.85	9.576%	$128.0396	$128.04	$128.05	$128.00
7 purchase totals =	$861.17		$939.8397	$939.84	$939.75	$939.90