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	$90.35	8.542%	$98.0677	$98.07	$98.05	$98.10
Purchase #2	$165.65	8.262%	$179.336	$179.34	$179.35	$179.30
Purchase #3	$194.60	12.673%	$219.2617	$219.26	$219.25	$219.30
Purchase #4	$82.27	10.231%	$90.687	$90.69	$90.70	$90.70
Purchase #5	$122.33	4.138%	$127.392	$127.39	$127.40	$127.40
Purchase #6	$86.91	5.666%	$91.8343	$91.83	$91.85	$91.80
Purchase #7	$46.40	12.548%	$52.2223	$52.22	$52.20	$52.20
7 purchase totals =	$788.51		$858.8010	$858.80	$858.80	$858.80