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	$145.40	11.761%	$162.5005	$162.50	$162.50	$162.50
Purchase #2	$173.32	5.191%	$182.317	$182.32	$182.30	$182.30
Purchase #3	$128.41	10.563%	$141.9739	$141.97	$141.95	$142.00
Purchase #4	$6.32	12.622%	$7.1177	$7.12	$7.10	$7.10
Purchase #5	$162.91	4.634%	$170.4592	$170.46	$170.45	$170.50
Purchase #6	$7.48	4.784%	$7.8378	$7.84	$7.85	$7.80
Purchase #7	$150.53	6.308%	$160.0254	$160.03	$160.05	$160.00
7 purchase totals =	$774.37		$832.2315	$832.24	$832.20	$832.20