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	$15.93	12.340%	$17.8958	$17.90	$17.90	$17.90
Purchase #2	$58.39	3.826%	$60.624	$60.62	$60.60	$60.60
Purchase #3	$196.59	3.858%	$204.1744	$204.17	$204.15	$204.20
Purchase #4	$178.94	5.160%	$188.1733	$188.17	$188.15	$188.20
Purchase #5	$239.40	10.409%	$264.3191	$264.32	$264.30	$264.30
Purchase #6	$78.97	7.844%	$85.1644	$85.16	$85.15	$85.20
Purchase #7	$180.96	4.525%	$189.1484	$189.15	$189.15	$189.10
7 purchase totals =	$949.18		$1,009.4994	$1,009.49	$1,009.40	$1,009.50