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	$48.76	3.728%	$50.5778	$50.58	$50.60	$50.60
Purchase #2	$64.58	13.119%	$73.0523	$73.05	$73.05	$73.10
Purchase #3	$220.67	9.585%	$241.8212	$241.82	$241.80	$241.80
Purchase #4	$76.43	12.336%	$85.8584	$85.86	$85.85	$85.90
Purchase #5	$221.76	7.573%	$238.5539	$238.55	$238.55	$238.60
Purchase #6	$38.25	11.568%	$42.6748	$42.67	$42.65	$42.70
Purchase #7	$167.43	9.373%	$183.1232	$183.12	$183.10	$183.10
7 purchase totals =	$837.88		$915.6616	$915.65	$915.60	$915.80