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	$62.55	13.190%	$70.8003	$70.80	$70.80	$70.80
Purchase #2	$149.83	9.559%	$164.1522	$164.15	$164.15	$164.20
Purchase #3	$158.88	11.265%	$176.7778	$176.78	$176.80	$176.80
Purchase #4	$132.41	6.692%	$141.2709	$141.27	$141.25	$141.30
Purchase #5	$107.62	3.529%	$111.4179	$111.42	$111.40	$111.40
Purchase #6	$82.72	13.562%	$93.9385	$93.94	$93.95	$93.90
Purchase #7	$147.38	5.831%	$155.9737	$155.97	$155.95	$156.00
7 purchase totals =	$841.39		$914.3313	$914.33	$914.30	$914.40