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	$156.56	10.124%	$172.4101	$172.41	$172.40	$172.40
Purchase #2	$125.62	4.382%	$131.1247	$131.12	$131.10	$131.10
Purchase #3	$246.39	13.461%	$279.5566	$279.56	$279.55	$279.60
Purchase #4	$37.43	8.601%	$40.6494	$40.65	$40.65	$40.60
Purchase #5	$67.73	13.623%	$76.9569	$76.96	$76.95	$77.00
Purchase #6	$230.87	7.803%	$248.8848	$248.88	$248.90	$248.90
Purchase #7	$230.80	3.681%	$239.2957	$239.30	$239.30	$239.30
7 purchase totals =	$1,095.40		$1,188.8782	$1,188.88	$1,188.85	$1,188.90