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	$29.71	11.702%	$33.1867	$33.19	$33.20	$33.20
Purchase #2	$112.46	3.229%	$116.0913	$116.09	$116.10	$116.10
Purchase #3	$161.91	6.369%	$172.222	$172.22	$172.20	$172.20
Purchase #4	$223.59	7.862%	$241.1686	$241.17	$241.15	$241.20
Purchase #5	$68.96	13.795%	$78.473	$78.47	$78.45	$78.50
Purchase #6	$27.34	10.788%	$30.2894	$30.29	$30.30	$30.30
Purchase #7	$175.75	6.866%	$187.817	$187.82	$187.80	$187.80
7 purchase totals =	$799.72		$859.2480	$859.25	$859.20	$859.30