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	$79.36	12.357%	$89.1665	$89.17	$89.15	$89.20
Purchase #2	$38.90	13.831%	$44.2803	$44.28	$44.30	$44.30
Purchase #3	$50.39	3.162%	$51.9833	$51.98	$52.00	$52.00
Purchase #4	$224.82	13.777%	$255.7935	$255.79	$255.80	$255.80
Purchase #5	$135.34	11.458%	$150.8473	$150.85	$150.85	$150.80
Purchase #6	$190.75	3.692%	$197.7925	$197.79	$197.80	$197.80
Purchase #7	$40.78	6.670%	$43.5	$43.50	$43.50	$43.50
7 purchase totals =	$760.34		$833.3634	$833.36	$833.40	$833.40