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	$10.83	9.222%	$11.8287	$11.83	$11.85	$11.80
Purchase #2	$247.69	12.615%	$278.9361	$278.94	$278.95	$278.90
Purchase #3	$89.86	12.807%	$101.3684	$101.37	$101.35	$101.40
Purchase #4	$66.79	8.640%	$72.5607	$72.56	$72.55	$72.60
Purchase #5	$127.86	13.726%	$145.4101	$145.41	$145.40	$145.40
Purchase #6	$243.50	7.732%	$262.3274	$262.33	$262.35	$262.30
Purchase #7	$191.61	8.251%	$207.4197	$207.42	$207.40	$207.40
7 purchase totals =	$978.14		$1,079.8511	$1,079.86	$1,079.85	$1,079.80