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	$158.31	7.469%	$170.1342	$170.13	$170.15	$170.10
Purchase #2	$146.68	6.661%	$156.4504	$156.45	$156.45	$156.50
Purchase #3	$56.79	10.550%	$62.7813	$62.78	$62.80	$62.80
Purchase #4	$209.28	3.650%	$216.9187	$216.92	$216.90	$216.90
Purchase #5	$156.46	7.466%	$168.1413	$168.14	$168.15	$168.10
Purchase #6	$47.58	11.665%	$53.1302	$53.13	$53.15	$53.10
Purchase #7	$105.25	6.263%	$111.8418	$111.84	$111.85	$111.80
7 purchase totals =	$880.35		$939.3979	$939.39	$939.45	$939.30