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	$166.78	7.574%	$179.4119	$179.41	$179.40	$179.40
Purchase #2	$122.54	12.118%	$137.3894	$137.39	$137.40	$137.40
Purchase #3	$94.29	9.739%	$103.4729	$103.47	$103.45	$103.50
Purchase #4	$52.41	7.680%	$56.4351	$56.44	$56.45	$56.40
Purchase #5	$125.88	5.777%	$133.1521	$133.15	$133.15	$133.20
Purchase #6	$137.42	7.322%	$147.4819	$147.48	$147.50	$147.50
Purchase #7	$112.93	9.132%	$123.2428	$123.24	$123.25	$123.20
7 purchase totals =	$812.25		$880.5861	$880.58	$880.60	$880.60