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	$142.65	4.300%	$148.784	$148.78	$148.80	$148.80
Purchase #2	$132.55	5.554%	$139.9118	$139.91	$139.90	$139.90
Purchase #3	$37.80	12.353%	$42.4694	$42.47	$42.45	$42.50
Purchase #4	$34.98	7.125%	$37.4723	$37.47	$37.45	$37.50
Purchase #5	$22.26	4.809%	$23.3305	$23.33	$23.35	$23.30
Purchase #6	$95.85	5.212%	$100.8457	$100.85	$100.85	$100.80
Purchase #7	$43.78	4.228%	$45.631	$45.63	$45.65	$45.60
7 purchase totals =	$509.87		$538.4447	$538.44	$538.45	$538.40