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	$19.88	7.838%	$21.4382	$21.44	$21.45	$21.40
Purchase #2	$168.49	8.796%	$183.3104	$183.31	$183.30	$183.30
Purchase #3	$206.55	11.429%	$230.1566	$230.16	$230.15	$230.20
Purchase #4	$121.85	4.428%	$127.2455	$127.25	$127.25	$127.20
Purchase #5	$80.86	7.311%	$86.7717	$86.77	$86.75	$86.80
Purchase #6	$199.67	11.521%	$222.674	$222.67	$222.65	$222.70
Purchase #7	$196.95	4.225%	$205.2711	$205.27	$205.25	$205.30
7 purchase totals =	$994.25		$1,076.8675	$1,076.87	$1,076.80	$1,076.90