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	$72.54	7.711%	$78.1336	$78.13	$78.15	$78.10
Purchase #2	$7.89	7.120%	$8.4518	$8.45	$8.45	$8.50
Purchase #3	$226.78	13.595%	$257.6107	$257.61	$257.60	$257.60
Purchase #4	$39.33	5.831%	$41.6233	$41.62	$41.60	$41.60
Purchase #5	$25.54	5.267%	$26.8852	$26.89	$26.90	$26.90
Purchase #6	$93.93	13.388%	$106.5053	$106.51	$106.50	$106.50
Purchase #7	$61.59	6.585%	$65.6457	$65.65	$65.65	$65.60
7 purchase totals =	$527.60		$584.8556	$584.86	$584.85	$584.80