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	$50.34	12.614%	$56.6899	$56.69	$56.70	$56.70
Purchase #2	$162.63	5.527%	$171.6186	$171.62	$171.60	$171.60
Purchase #3	$180.33	4.173%	$187.8552	$187.86	$187.85	$187.90
Purchase #4	$163.38	5.550%	$172.4476	$172.45	$172.45	$172.40
Purchase #5	$225.96	9.739%	$247.9662	$247.97	$247.95	$248.00
Purchase #6	$139.28	5.142%	$146.4418	$146.44	$146.45	$146.40
Purchase #7	$99.47	13.439%	$112.8378	$112.84	$112.85	$112.80
7 purchase totals =	$1,021.39		$1,095.8571	$1,095.87	$1,095.85	$1,095.80