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	$220.46	4.630%	$230.6673	$230.67	$230.65	$230.70
Purchase #2	$202.97	10.644%	$224.5741	$224.57	$224.55	$224.60
Purchase #3	$64.52	11.379%	$71.8617	$71.86	$71.85	$71.90
Purchase #4	$209.65	6.341%	$222.9439	$222.94	$222.95	$222.90
Purchase #5	$81.59	13.811%	$92.8584	$92.86	$92.85	$92.90
Purchase #6	$138.27	9.348%	$151.1955	$151.20	$151.20	$151.20
Purchase #7	$78.38	8.835%	$85.3049	$85.30	$85.30	$85.30
7 purchase totals =	$995.84		$1,079.4058	$1,079.40	$1,079.35	$1,079.50