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	$21.50	4.332%	$22.4314	$22.43	$22.45	$22.40
Purchase #2	$86.72	10.502%	$95.8273	$95.83	$95.85	$95.80
Purchase #3	$99.85	7.706%	$107.5444	$107.54	$107.55	$107.50
Purchase #4	$119.97	6.374%	$127.6169	$127.62	$127.60	$127.60
Purchase #5	$73.73	6.272%	$78.3543	$78.35	$78.35	$78.40
Purchase #6	$204.71	9.566%	$224.2926	$224.29	$224.30	$224.30
Purchase #7	$227.46	3.243%	$234.8365	$234.84	$234.85	$234.80
7 purchase totals =	$833.94		$890.9034	$890.90	$890.95	$890.80