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	$142.54	13.730%	$162.1107	$162.11	$162.10	$162.10
Purchase #2	$127.63	8.323%	$138.2526	$138.25	$138.25	$138.30
Purchase #3	$49.77	9.762%	$54.6285	$54.63	$54.65	$54.60
Purchase #4	$100.53	3.777%	$104.327	$104.33	$104.35	$104.30
Purchase #5	$42.73	6.127%	$45.3481	$45.35	$45.35	$45.30
Purchase #6	$217.58	8.164%	$235.3432	$235.34	$235.35	$235.30
Purchase #7	$105.49	5.444%	$111.2329	$111.23	$111.25	$111.20
7 purchase totals =	$786.27		$851.2430	$851.24	$851.30	$851.10