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	$74.52	11.360%	$82.9855	$82.99	$83.00	$83.00
Purchase #2	$76.76	11.334%	$85.46	$85.46	$85.45	$85.50
Purchase #3	$121.73	7.757%	$131.1726	$131.17	$131.15	$131.20
Purchase #4	$100.68	13.438%	$114.2094	$114.21	$114.20	$114.20
Purchase #5	$142.77	7.849%	$153.976	$153.98	$154.00	$154.00
Purchase #6	$35.30	10.848%	$39.1293	$39.13	$39.15	$39.10
Purchase #7	$64.30	13.778%	$73.1593	$73.16	$73.15	$73.20
7 purchase totals =	$616.06		$680.0921	$680.10	$680.10	$680.20