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	$63.91	9.360%	$69.892	$69.89	$69.90	$69.90
Purchase #2	$119.61	9.774%	$131.3007	$131.30	$131.30	$131.30
Purchase #3	$86.40	10.724%	$95.6655	$95.67	$95.65	$95.70
Purchase #4	$91.66	9.322%	$100.2045	$100.20	$100.20	$100.20
Purchase #5	$18.33	9.663%	$20.1012	$20.10	$20.10	$20.10
Purchase #6	$190.75	13.176%	$215.8832	$215.88	$215.90	$215.90
Purchase #7	$158.92	11.272%	$176.8335	$176.83	$176.85	$176.80
7 purchase totals =	$729.58		$809.8806	$809.87	$809.90	$809.90