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	$143.49	11.220%	$159.5896	$159.59	$159.60	$159.60
Purchase #2	$212.88	4.180%	$221.7784	$221.78	$221.80	$221.80
Purchase #3	$28.66	12.656%	$32.2872	$32.29	$32.30	$32.30
Purchase #4	$142.61	13.716%	$162.1704	$162.17	$162.15	$162.20
Purchase #5	$41.48	8.507%	$45.0087	$45.01	$45.00	$45.00
Purchase #6	$94.99	8.849%	$103.3957	$103.40	$103.40	$103.40
Purchase #7	$91.96	9.486%	$100.6833	$100.68	$100.70	$100.70
7 purchase totals =	$756.07		$824.9133	$824.92	$824.95	$825.00