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	$178.58	5.154%	$187.784	$187.78	$187.80	$187.80
Purchase #2	$53.94	6.199%	$57.2837	$57.28	$57.30	$57.30
Purchase #3	$217.29	6.212%	$230.7881	$230.79	$230.80	$230.80
Purchase #4	$91.37	12.844%	$103.1056	$103.11	$103.10	$103.10
Purchase #5	$79.72	3.380%	$82.4145	$82.41	$82.40	$82.40
Purchase #6	$119.64	6.692%	$127.6463	$127.65	$127.65	$127.60
Purchase #7	$162.86	11.319%	$181.2941	$181.29	$181.30	$181.30
7 purchase totals =	$903.40		$970.3163	$970.31	$970.35	$970.30