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	$157.80	7.489%	$169.6176	$169.62	$169.60	$169.60
Purchase #2	$135.89	4.761%	$142.3597	$142.36	$142.35	$142.40
Purchase #3	$36.66	12.608%	$41.2821	$41.28	$41.30	$41.30
Purchase #4	$89.52	11.274%	$99.6125	$99.61	$99.60	$99.60
Purchase #5	$86.85	4.557%	$90.8078	$90.81	$90.80	$90.80
Purchase #6	$58.60	3.788%	$60.8198	$60.82	$60.80	$60.80
Purchase #7	$16.91	4.448%	$17.6622	$17.66	$17.65	$17.70
7 purchase totals =	$582.23		$622.1617	$622.16	$622.10	$622.20