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	$80.92	3.649%	$83.8728	$83.87	$83.85	$83.90
Purchase #2	$91.74	7.388%	$98.5178	$98.52	$98.50	$98.50
Purchase #3	$92.59	12.710%	$104.3582	$104.36	$104.35	$104.40
Purchase #4	$43.51	4.340%	$45.3983	$45.40	$45.40	$45.40
Purchase #5	$53.32	7.783%	$57.4699	$57.47	$57.45	$57.50
Purchase #6	$67.26	4.371%	$70.1999	$70.20	$70.20	$70.20
Purchase #7	$161.79	5.690%	$170.9959	$171.00	$171.00	$171.00
7 purchase totals =	$591.13		$630.8128	$630.82	$630.75	$630.90