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	$147.65	7.749%	$159.0914	$159.09	$159.10	$159.10
Purchase #2	$47.66	8.868%	$51.8865	$51.89	$51.90	$51.90
Purchase #3	$145.34	4.278%	$151.5576	$151.56	$151.55	$151.60
Purchase #4	$244.60	9.344%	$267.4554	$267.46	$267.45	$267.50
Purchase #5	$40.42	4.183%	$42.1108	$42.11	$42.10	$42.10
Purchase #6	$126.67	12.590%	$142.6178	$142.62	$142.60	$142.60
Purchase #7	$166.91	5.137%	$175.4842	$175.48	$175.50	$175.50
7 purchase totals =	$919.25		$990.2037	$990.21	$990.20	$990.30