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	$150.89	6.637%	$160.9046	$160.90	$160.90	$160.90
Purchase #2	$183.98	7.404%	$197.6019	$197.60	$197.60	$197.60
Purchase #3	$166.78	10.208%	$183.8049	$183.80	$183.80	$183.80
Purchase #4	$228.69	12.125%	$256.4187	$256.42	$256.40	$256.40
Purchase #5	$228.66	11.630%	$255.2532	$255.25	$255.25	$255.30
Purchase #6	$64.50	11.255%	$71.7595	$71.76	$71.75	$71.80
Purchase #7	$150.38	3.343%	$155.4072	$155.41	$155.40	$155.40
7 purchase totals =	$1,173.88		$1,281.1500	$1,281.14	$1,281.10	$1,281.20