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	$25.37	10.838%	$28.1196	$28.12	$28.10	$28.10
Purchase #2	$104.35	8.155%	$112.8597	$112.86	$112.85	$112.90
Purchase #3	$12.28	12.563%	$13.8227	$13.82	$13.80	$13.80
Purchase #4	$210.45	3.172%	$217.1255	$217.13	$217.15	$217.10
Purchase #5	$94.98	8.677%	$103.2214	$103.22	$103.20	$103.20
Purchase #6	$57.72	6.633%	$61.5486	$61.55	$61.55	$61.50
Purchase #7	$37.65	9.557%	$41.2482	$41.25	$41.25	$41.20
7 purchase totals =	$542.80		$577.9457	$577.95	$577.90	$577.80