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	$135.45	6.464%	$144.2055	$144.21	$144.20	$144.20
Purchase #2	$171.58	6.548%	$182.8151	$182.82	$182.80	$182.80
Purchase #3	$226.71	10.512%	$250.5418	$250.54	$250.55	$250.50
Purchase #4	$220.88	9.180%	$241.1568	$241.16	$241.15	$241.20
Purchase #5	$83.45	7.749%	$89.9165	$89.92	$89.90	$89.90
Purchase #6	$177.56	12.683%	$200.0799	$200.08	$200.10	$200.10
Purchase #7	$172.54	9.646%	$189.1832	$189.18	$189.20	$189.20
7 purchase totals =	$1,188.17		$1,297.8988	$1,297.91	$1,297.90	$1,297.90