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	$144.53	6.623%	$154.1022	$154.10	$154.10	$154.10
Purchase #2	$101.56	9.302%	$111.0071	$111.01	$111.00	$111.00
Purchase #3	$69.55	10.659%	$76.9633	$76.96	$76.95	$77.00
Purchase #4	$69.60	10.104%	$76.6324	$76.63	$76.65	$76.60
Purchase #5	$139.70	11.718%	$156.07	$156.07	$156.05	$156.10
Purchase #6	$37.96	6.278%	$40.3431	$40.34	$40.35	$40.30
Purchase #7	$233.34	3.401%	$241.2759	$241.28	$241.30	$241.30
7 purchase totals =	$796.24		$856.3940	$856.39	$856.40	$856.40