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	$54.42	10.330%	$60.0416	$60.04	$60.05	$60.00
Purchase #2	$67.31	7.375%	$72.2741	$72.27	$72.25	$72.30
Purchase #3	$52.82	13.559%	$59.9819	$59.98	$60.00	$60.00
Purchase #4	$241.89	8.161%	$261.6306	$261.63	$261.65	$261.60
Purchase #5	$25.78	3.834%	$26.7684	$26.77	$26.75	$26.80
Purchase #6	$47.37	11.139%	$52.6465	$52.65	$52.65	$52.60
Purchase #7	$75.93	12.233%	$85.2185	$85.22	$85.20	$85.20
7 purchase totals =	$565.52		$618.5616	$618.56	$618.55	$618.50