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	$41.48	10.419%	$45.8018	$45.80	$45.80	$45.80
Purchase #2	$144.47	11.577%	$161.1953	$161.20	$161.20	$161.20
Purchase #3	$40.80	10.724%	$45.1754	$45.18	$45.20	$45.20
Purchase #4	$106.99	6.852%	$114.321	$114.32	$114.30	$114.30
Purchase #5	$57.47	7.653%	$61.8682	$61.87	$61.85	$61.90
Purchase #6	$159.38	9.368%	$174.3107	$174.31	$174.30	$174.30
Purchase #7	$225.54	13.373%	$255.7015	$255.70	$255.70	$255.70
7 purchase totals =	$776.13		$858.3739	$858.38	$858.35	$858.40