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	$9.81	13.719%	$11.1558	$11.16	$11.15	$11.20
Purchase #2	$191.53	4.822%	$200.7656	$200.77	$200.75	$200.80
Purchase #3	$94.93	11.473%	$105.8213	$105.82	$105.80	$105.80
Purchase #4	$186.53	6.400%	$198.4679	$198.47	$198.45	$198.50
Purchase #5	$136.57	7.675%	$147.0517	$147.05	$147.05	$147.10
Purchase #6	$196.59	6.649%	$209.6613	$209.66	$209.65	$209.70
Purchase #7	$25.51	8.263%	$27.6179	$27.62	$27.60	$27.60
7 purchase totals =	$841.47		$900.5415	$900.55	$900.45	$900.70