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	$19.57	4.180%	$20.388	$20.39	$20.40	$20.40
Purchase #2	$153.93	6.275%	$163.5891	$163.59	$163.60	$163.60
Purchase #3	$151.72	10.284%	$167.3229	$167.32	$167.30	$167.30
Purchase #4	$95.36	10.713%	$105.5759	$105.58	$105.60	$105.60
Purchase #5	$81.99	10.587%	$90.6703	$90.67	$90.65	$90.70
Purchase #6	$138.58	7.828%	$149.428	$149.43	$149.45	$149.40
Purchase #7	$136.48	11.562%	$152.2598	$152.26	$152.25	$152.30
7 purchase totals =	$777.63		$849.2340	$849.24	$849.25	$849.30