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	$128.26	4.773%	$134.3818	$134.38	$134.40	$134.40
Purchase #2	$139.73	9.427%	$152.9023	$152.90	$152.90	$152.90
Purchase #3	$107.68	4.149%	$112.1476	$112.15	$112.15	$112.10
Purchase #4	$27.88	13.481%	$31.6385	$31.64	$31.65	$31.60
Purchase #5	$134.68	12.747%	$151.8477	$151.85	$151.85	$151.80
Purchase #6	$172.46	10.248%	$190.1337	$190.13	$190.15	$190.10
Purchase #7	$80.90	3.513%	$83.742	$83.74	$83.75	$83.70
7 purchase totals =	$791.59		$856.7936	$856.79	$856.85	$856.60