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	$87.58	3.791%	$90.9002	$90.90	$90.90	$90.90
Purchase #2	$9.76	8.118%	$10.5523	$10.55	$10.55	$10.60
Purchase #3	$38.80	4.798%	$40.6616	$40.66	$40.65	$40.70
Purchase #4	$55.50	4.396%	$57.9398	$57.94	$57.95	$57.90
Purchase #5	$145.69	6.109%	$154.5902	$154.59	$154.60	$154.60
Purchase #6	$161.83	9.198%	$176.7151	$176.72	$176.70	$176.70
Purchase #7	$249.56	4.376%	$260.4807	$260.48	$260.50	$260.50
7 purchase totals =	$748.72		$791.8399	$791.84	$791.85	$791.90