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	$230.57	10.655%	$255.1372	$255.14	$255.15	$255.10
Purchase #2	$173.27	4.768%	$181.5315	$181.53	$181.55	$181.50
Purchase #3	$250.27	5.806%	$264.8007	$264.80	$264.80	$264.80
Purchase #4	$43.79	12.574%	$49.2962	$49.30	$49.30	$49.30
Purchase #5	$35.40	11.259%	$39.3857	$39.39	$39.40	$39.40
Purchase #6	$242.98	6.124%	$257.8601	$257.86	$257.85	$257.90
Purchase #7	$31.51	7.371%	$33.8326	$33.83	$33.85	$33.80
7 purchase totals =	$1,007.79		$1,081.8440	$1,081.85	$1,081.90	$1,081.80