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	$27.53	7.307%	$29.5416	$29.54	$29.55	$29.50
Purchase #2	$139.75	11.558%	$155.9023	$155.90	$155.90	$155.90
Purchase #3	$49.83	10.175%	$54.9002	$54.90	$54.90	$54.90
Purchase #4	$138.95	3.154%	$143.3325	$143.33	$143.35	$143.30
Purchase #5	$173.56	7.771%	$187.0473	$187.05	$187.05	$187.00
Purchase #6	$53.80	10.180%	$59.2768	$59.28	$59.30	$59.30
Purchase #7	$113.77	9.179%	$124.2129	$124.21	$124.20	$124.20
7 purchase totals =	$697.19		$754.2136	$754.21	$754.25	$754.10