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	$31.73	6.439%	$33.7731	$33.77	$33.75	$33.80
Purchase #2	$37.87	5.261%	$39.8623	$39.86	$39.85	$39.90
Purchase #3	$110.69	8.534%	$120.1363	$120.14	$120.15	$120.10
Purchase #4	$143.43	3.415%	$148.3281	$148.33	$148.35	$148.30
Purchase #5	$181.51	10.537%	$200.6357	$200.64	$200.65	$200.60
Purchase #6	$114.75	13.702%	$130.473	$130.47	$130.45	$130.50
Purchase #7	$134.54	7.724%	$144.9319	$144.93	$144.95	$144.90
7 purchase totals =	$754.52		$818.1404	$818.14	$818.15	$818.10