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	$130.47	12.345%	$146.5765	$146.58	$146.60	$146.60
Purchase #2	$81.30	9.550%	$89.0642	$89.06	$89.05	$89.10
Purchase #3	$25.48	11.778%	$28.481	$28.48	$28.50	$28.50
Purchase #4	$142.65	7.239%	$152.9764	$152.98	$153.00	$153.00
Purchase #5	$132.47	4.481%	$138.406	$138.41	$138.40	$138.40
Purchase #6	$44.33	7.713%	$47.7492	$47.75	$47.75	$47.70
Purchase #7	$135.83	11.552%	$151.5211	$151.52	$151.50	$151.50
7 purchase totals =	$692.53		$754.7744	$754.78	$754.80	$754.80