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	$109.60	11.745%	$122.4725	$122.47	$122.45	$122.50
Purchase #2	$160.86	11.582%	$179.4908	$179.49	$179.50	$179.50
Purchase #3	$211.45	7.598%	$227.516	$227.52	$227.50	$227.50
Purchase #4	$83.67	3.823%	$86.8687	$86.87	$86.85	$86.90
Purchase #5	$109.65	12.807%	$123.6929	$123.69	$123.70	$123.70
Purchase #6	$149.64	5.337%	$157.6263	$157.63	$157.65	$157.60
Purchase #7	$79.34	11.521%	$88.4808	$88.48	$88.50	$88.50
7 purchase totals =	$904.21		$986.1480	$986.15	$986.15	$986.20