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	$134.53	3.466%	$139.1928	$139.19	$139.20	$139.20
Purchase #2	$97.42	3.206%	$100.5433	$100.54	$100.55	$100.50
Purchase #3	$81.86	13.399%	$92.8284	$92.83	$92.85	$92.80
Purchase #4	$93.44	7.387%	$100.3424	$100.34	$100.35	$100.30
Purchase #5	$159.84	12.343%	$179.5691	$179.57	$179.55	$179.60
Purchase #6	$10.86	5.553%	$11.4631	$11.46	$11.45	$11.50
Purchase #7	$23.55	3.130%	$24.2871	$24.29	$24.30	$24.30
7 purchase totals =	$601.50		$648.2262	$648.22	$648.25	$648.20