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	$44.87	3.640%	$46.5033	$46.50	$46.50	$46.50
Purchase #2	$78.84	5.869%	$83.4671	$83.47	$83.45	$83.50
Purchase #3	$172.43	13.416%	$195.5632	$195.56	$195.55	$195.60
Purchase #4	$115.36	7.768%	$124.3212	$124.32	$124.30	$124.30
Purchase #5	$127.59	5.733%	$134.9047	$134.90	$134.90	$134.90
Purchase #6	$43.71	12.799%	$49.3044	$49.30	$49.30	$49.30
Purchase #7	$99.38	9.832%	$109.151	$109.15	$109.15	$109.20
7 purchase totals =	$682.18		$743.2149	$743.20	$743.15	$743.30