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	$68.82	13.566%	$78.1561	$78.16	$78.15	$78.20
Purchase #2	$177.77	9.251%	$194.2155	$194.22	$194.20	$194.20
Purchase #3	$26.71	10.691%	$29.5656	$29.57	$29.55	$29.60
Purchase #4	$174.42	6.127%	$185.1067	$185.11	$185.10	$185.10
Purchase #5	$137.44	13.702%	$156.272	$156.27	$156.25	$156.30
Purchase #6	$156.37	8.154%	$169.1204	$169.12	$169.10	$169.10
Purchase #7	$123.29	3.434%	$127.5238	$127.52	$127.50	$127.50
7 purchase totals =	$864.82		$939.9601	$939.97	$939.85	$940.00