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	$9.38	10.702%	$10.3838	$10.38	$10.40	$10.40
Purchase #2	$63.95	3.319%	$66.0725	$66.07	$66.05	$66.10
Purchase #3	$20.88	8.461%	$22.6467	$22.65	$22.65	$22.60
Purchase #4	$28.45	10.857%	$31.5388	$31.54	$31.55	$31.50
Purchase #5	$120.98	12.779%	$136.44	$136.44	$136.45	$136.40
Purchase #6	$187.30	3.695%	$194.2207	$194.22	$194.20	$194.20
Purchase #7	$62.72	13.386%	$71.1157	$71.12	$71.10	$71.10
7 purchase totals =	$493.66		$532.4182	$532.42	$532.40	$532.30