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	$7.57	9.806%	$8.3123	$8.31	$8.30	$8.30
Purchase #2	$195.89	4.336%	$204.3838	$204.38	$204.40	$204.40
Purchase #3	$32.63	6.337%	$34.6978	$34.70	$34.70	$34.70
Purchase #4	$140.25	11.323%	$156.1305	$156.13	$156.15	$156.10
Purchase #5	$82.29	8.870%	$89.5891	$89.59	$89.60	$89.60
Purchase #6	$80.39	4.393%	$83.9215	$83.92	$83.90	$83.90
Purchase #7	$100.73	8.173%	$108.9627	$108.96	$108.95	$109.00
7 purchase totals =	$639.75		$685.9977	$685.99	$686.00	$686.00