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	$32.71	3.386%	$33.8176	$33.82	$33.80	$33.80
Purchase #2	$150.45	9.715%	$165.0662	$165.07	$165.05	$165.10
Purchase #3	$158.85	8.502%	$172.3554	$172.36	$172.35	$172.40
Purchase #4	$210.55	13.190%	$238.3215	$238.32	$238.30	$238.30
Purchase #5	$188.72	11.620%	$210.6493	$210.65	$210.65	$210.60
Purchase #6	$71.61	5.854%	$75.802	$75.80	$75.80	$75.80
Purchase #7	$158.92	10.448%	$175.524	$175.52	$175.50	$175.50
7 purchase totals =	$971.81		$1,071.5360	$1,071.54	$1,071.45	$1,071.50