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	$29.84	11.630%	$33.3104	$33.31	$33.30	$33.30
Purchase #2	$85.46	10.791%	$94.682	$94.68	$94.70	$94.70
Purchase #3	$164.55	12.480%	$185.0858	$185.09	$185.10	$185.10
Purchase #4	$36.73	3.312%	$37.9465	$37.95	$37.95	$37.90
Purchase #5	$41.31	9.608%	$45.2791	$45.28	$45.30	$45.30
Purchase #6	$51.66	5.343%	$54.4202	$54.42	$54.40	$54.40
Purchase #7	$178.87	8.561%	$194.1831	$194.18	$194.20	$194.20
7 purchase totals =	$588.42		$644.9071	$644.91	$644.95	$644.90