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	$172.92	10.735%	$191.483	$191.48	$191.50	$191.50
Purchase #2	$55.52	3.167%	$57.2783	$57.28	$57.30	$57.30
Purchase #3	$34.47	11.822%	$38.545	$38.55	$38.55	$38.50
Purchase #4	$49.62	6.450%	$52.8205	$52.82	$52.80	$52.80
Purchase #5	$87.52	9.799%	$96.0961	$96.10	$96.10	$96.10
Purchase #6	$193.44	13.454%	$219.4654	$219.47	$219.45	$219.50
Purchase #7	$233.66	9.178%	$255.1053	$255.11	$255.10	$255.10
7 purchase totals =	$827.15		$910.7936	$910.81	$910.80	$910.80