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	$35.47	9.496%	$38.8382	$38.84	$38.85	$38.80
Purchase #2	$134.89	5.274%	$142.0041	$142.00	$142.00	$142.00
Purchase #3	$36.33	8.669%	$39.4794	$39.48	$39.50	$39.50
Purchase #4	$139.92	4.626%	$146.3927	$146.39	$146.40	$146.40
Purchase #5	$34.90	12.652%	$39.3155	$39.32	$39.30	$39.30
Purchase #6	$91.42	6.182%	$97.0716	$97.07	$97.05	$97.10
Purchase #7	$88.47	11.437%	$98.5883	$98.59	$98.60	$98.60
7 purchase totals =	$561.40		$601.6898	$601.69	$601.70	$601.70