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	$90.28	9.789%	$99.1175	$99.12	$99.10	$99.10
Purchase #2	$161.75	3.861%	$167.9952	$168.00	$168.00	$168.00
Purchase #3	$15.50	6.324%	$16.4802	$16.48	$16.50	$16.50
Purchase #4	$192.34	10.579%	$212.6876	$212.69	$212.70	$212.70
Purchase #5	$91.73	8.275%	$99.3207	$99.32	$99.30	$99.30
Purchase #6	$110.72	12.713%	$124.7958	$124.80	$124.80	$124.80
Purchase #7	$104.92	6.224%	$111.4502	$111.45	$111.45	$111.50
7 purchase totals =	$767.24		$831.8472	$831.86	$831.85	$831.90