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	$150.69	9.463%	$164.9498	$164.95	$164.95	$164.90
Purchase #2	$145.55	11.142%	$161.7672	$161.77	$161.75	$161.80
Purchase #3	$122.69	13.535%	$139.2961	$139.30	$139.30	$139.30
Purchase #4	$35.52	7.669%	$38.244	$38.24	$38.25	$38.20
Purchase #5	$228.51	7.240%	$245.0541	$245.05	$245.05	$245.10
Purchase #6	$224.28	3.837%	$232.8856	$232.89	$232.90	$232.90
Purchase #7	$96.53	9.182%	$105.3934	$105.39	$105.40	$105.40
7 purchase totals =	$1,003.77		$1,087.5902	$1,087.59	$1,087.60	$1,087.60