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	$40.29	6.236%	$42.8025	$42.80	$42.80	$42.80
Purchase #2	$139.42	12.317%	$156.5924	$156.59	$156.60	$156.60
Purchase #3	$33.92	11.125%	$37.6936	$37.69	$37.70	$37.70
Purchase #4	$15.74	3.607%	$16.3077	$16.31	$16.30	$16.30
Purchase #5	$174.53	9.142%	$190.4855	$190.49	$190.50	$190.50
Purchase #6	$60.94	8.218%	$65.948	$65.95	$65.95	$65.90
Purchase #7	$124.93	6.230%	$132.7131	$132.71	$132.70	$132.70
7 purchase totals =	$589.77		$642.5428	$642.54	$642.55	$642.50