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	$150.82	11.803%	$168.6213	$168.62	$168.60	$168.60
Purchase #2	$195.83	7.577%	$210.668	$210.67	$210.65	$210.70
Purchase #3	$97.67	5.762%	$103.2977	$103.30	$103.30	$103.30
Purchase #4	$68.89	9.419%	$75.3787	$75.38	$75.40	$75.40
Purchase #5	$41.69	9.129%	$45.4959	$45.50	$45.50	$45.50
Purchase #6	$150.41	11.766%	$168.1072	$168.11	$168.10	$168.10
Purchase #7	$42.92	7.211%	$46.015	$46.02	$46.00	$46.00
7 purchase totals =	$748.23		$817.5838	$817.60	$817.55	$817.60