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	$57.45	8.105%	$62.1063	$62.11	$62.10	$62.10
Purchase #2	$97.26	11.628%	$108.5694	$108.57	$108.55	$108.60
Purchase #3	$79.67	11.572%	$88.8894	$88.89	$88.90	$88.90
Purchase #4	$38.38	9.245%	$41.9282	$41.93	$41.95	$41.90
Purchase #5	$58.99	7.501%	$63.4148	$63.41	$63.40	$63.40
Purchase #6	$83.59	8.139%	$90.3934	$90.39	$90.40	$90.40
Purchase #7	$129.59	12.219%	$145.4246	$145.42	$145.40	$145.40
7 purchase totals =	$544.93		$600.7261	$600.72	$600.70	$600.70