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	$9.30	12.811%	$10.4914	$10.49	$10.50	$10.50
Purchase #2	$211.36	10.647%	$233.8635	$233.86	$233.85	$233.90
Purchase #3	$128.57	5.862%	$136.1068	$136.11	$136.10	$136.10
Purchase #4	$215.80	10.412%	$238.2691	$238.27	$238.25	$238.30
Purchase #5	$13.80	13.156%	$15.6155	$15.62	$15.60	$15.60
Purchase #6	$117.61	11.618%	$131.2739	$131.27	$131.25	$131.30
Purchase #7	$32.84	10.588%	$36.3171	$36.32	$36.30	$36.30
7 purchase totals =	$729.28		$801.9373	$801.94	$801.85	$802.00