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	$18.80	9.517%	$20.5892	$20.59	$20.60	$20.60
Purchase #2	$226.63	10.606%	$250.6664	$250.67	$250.65	$250.70
Purchase #3	$132.38	8.494%	$143.6244	$143.62	$143.60	$143.60
Purchase #4	$57.50	12.859%	$64.8939	$64.89	$64.90	$64.90
Purchase #5	$95.27	10.305%	$105.0876	$105.09	$105.10	$105.10
Purchase #6	$99.27	11.436%	$110.6225	$110.62	$110.60	$110.60
Purchase #7	$178.73	11.255%	$198.8461	$198.85	$198.85	$198.80
7 purchase totals =	$808.58		$894.3301	$894.33	$894.30	$894.30