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	$83.87	7.490%	$90.1519	$90.15	$90.15	$90.20
Purchase #2	$21.64	5.833%	$22.9023	$22.90	$22.90	$22.90
Purchase #3	$177.25	4.108%	$184.5314	$184.53	$184.55	$184.50
Purchase #4	$72.37	8.748%	$78.7009	$78.70	$78.70	$78.70
Purchase #5	$100.83	12.222%	$113.1534	$113.15	$113.15	$113.20
Purchase #6	$104.59	8.429%	$113.4059	$113.41	$113.40	$113.40
Purchase #7	$124.46	10.473%	$137.4947	$137.49	$137.50	$137.50
7 purchase totals =	$685.01		$740.3405	$740.33	$740.35	$740.40