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	$57.91	3.241%	$59.7869	$59.79	$59.80	$59.80
Purchase #2	$248.80	13.415%	$282.1765	$282.18	$282.20	$282.20
Purchase #3	$99.32	12.365%	$111.6009	$111.60	$111.60	$111.60
Purchase #4	$22.69	7.383%	$24.3652	$24.37	$24.35	$24.40
Purchase #5	$217.92	10.213%	$240.1762	$240.18	$240.20	$240.20
Purchase #6	$206.44	9.678%	$226.4193	$226.42	$226.40	$226.40
Purchase #7	$74.94	13.496%	$85.0539	$85.05	$85.05	$85.10
7 purchase totals =	$928.02		$1,029.5789	$1,029.59	$1,029.60	$1,029.70