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	$159.97	12.402%	$179.8095	$179.81	$179.80	$179.80
Purchase #2	$58.79	4.556%	$61.4685	$61.47	$61.45	$61.50
Purchase #3	$208.29	8.636%	$226.2779	$226.28	$226.30	$226.30
Purchase #4	$84.40	7.281%	$90.5452	$90.55	$90.55	$90.50
Purchase #5	$142.75	6.848%	$152.5255	$152.53	$152.55	$152.50
Purchase #6	$33.43	6.426%	$35.5782	$35.58	$35.60	$35.60
Purchase #7	$90.65	8.785%	$98.6136	$98.61	$98.60	$98.60
7 purchase totals =	$778.28		$844.8184	$844.83	$844.85	$844.80