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	$175.41	8.219%	$189.8269	$189.83	$189.85	$189.80
Purchase #2	$128.25	10.365%	$141.5431	$141.54	$141.55	$141.50
Purchase #3	$111.98	9.855%	$123.0156	$123.02	$123.00	$123.00
Purchase #4	$156.74	6.407%	$166.7823	$166.78	$166.80	$166.80
Purchase #5	$115.64	6.566%	$123.2329	$123.23	$123.25	$123.20
Purchase #6	$50.90	3.487%	$52.6749	$52.67	$52.65	$52.70
Purchase #7	$56.30	13.203%	$63.7333	$63.73	$63.75	$63.70
7 purchase totals =	$795.22		$860.8090	$860.80	$860.85	$860.70