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	$155.61	7.274%	$166.9291	$166.93	$166.95	$166.90
Purchase #2	$32.83	12.738%	$37.0119	$37.01	$37.00	$37.00
Purchase #3	$147.76	8.582%	$160.4408	$160.44	$160.45	$160.40
Purchase #4	$235.42	10.800%	$260.8454	$260.85	$260.85	$260.80
Purchase #5	$50.33	5.836%	$53.2673	$53.27	$53.25	$53.30
Purchase #6	$21.29	4.390%	$22.2246	$22.22	$22.20	$22.20
Purchase #7	$167.41	7.422%	$179.8352	$179.84	$179.85	$179.80
7 purchase totals =	$810.65		$880.5543	$880.56	$880.55	$880.40