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	$129.39	12.579%	$145.666	$145.67	$145.65	$145.70
Purchase #2	$183.50	7.139%	$196.6001	$196.60	$196.60	$196.60
Purchase #3	$109.90	7.459%	$118.0974	$118.10	$118.10	$118.10
Purchase #4	$14.96	6.514%	$15.9345	$15.93	$15.95	$15.90
Purchase #5	$38.78	5.308%	$40.8384	$40.84	$40.85	$40.80
Purchase #6	$110.87	7.142%	$118.7883	$118.79	$118.80	$118.80
Purchase #7	$146.95	6.214%	$156.0815	$156.08	$156.10	$156.10
7 purchase totals =	$734.35		$792.0062	$792.01	$792.05	$792.00