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	$104.59	13.319%	$118.5203	$118.52	$118.50	$118.50
Purchase #2	$139.91	5.415%	$147.4861	$147.49	$147.50	$147.50
Purchase #3	$83.36	9.772%	$91.5059	$91.51	$91.50	$91.50
Purchase #4	$33.43	12.569%	$37.6318	$37.63	$37.65	$37.60
Purchase #5	$141.58	3.291%	$146.2394	$146.24	$146.25	$146.20
Purchase #6	$47.70	11.224%	$53.0538	$53.05	$53.05	$53.10
Purchase #7	$88.91	10.286%	$98.0553	$98.06	$98.05	$98.10
7 purchase totals =	$639.48		$692.4926	$692.50	$692.50	$692.50