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	$26.31	10.643%	$29.1102	$29.11	$29.10	$29.10
Purchase #2	$7.68	5.574%	$8.1081	$8.11	$8.10	$8.10
Purchase #3	$20.82	5.158%	$21.8939	$21.89	$21.90	$21.90
Purchase #4	$209.92	13.436%	$238.1249	$238.12	$238.10	$238.10
Purchase #5	$181.71	3.217%	$187.5556	$187.56	$187.55	$187.60
Purchase #6	$192.47	13.302%	$218.0724	$218.07	$218.05	$218.10
Purchase #7	$246.94	11.476%	$275.2788	$275.28	$275.30	$275.30
7 purchase totals =	$885.85		$978.1439	$978.14	$978.10	$978.20