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	$142.76	12.701%	$160.8919	$160.89	$160.90	$160.90
Purchase #2	$95.70	4.613%	$100.1146	$100.11	$100.10	$100.10
Purchase #3	$219.40	11.477%	$244.5805	$244.58	$244.60	$244.60
Purchase #4	$104.80	13.238%	$118.6734	$118.67	$118.65	$118.70
Purchase #5	$205.51	11.120%	$228.3627	$228.36	$228.35	$228.40
Purchase #6	$227.53	5.706%	$240.5129	$240.51	$240.50	$240.50
Purchase #7	$128.52	12.367%	$144.4141	$144.41	$144.40	$144.40
7 purchase totals =	$1,124.22		$1,237.5501	$1,237.53	$1,237.50	$1,237.60