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	$247.61	8.386%	$268.3746	$268.37	$268.35	$268.40
Purchase #2	$137.40	4.415%	$143.4662	$143.47	$143.45	$143.50
Purchase #3	$181.86	8.148%	$196.678	$196.68	$196.70	$196.70
Purchase #4	$172.93	4.571%	$180.8346	$180.83	$180.85	$180.80
Purchase #5	$235.32	9.653%	$258.0354	$258.04	$258.05	$258.00
Purchase #6	$58.81	11.521%	$65.5855	$65.59	$65.60	$65.60
Purchase #7	$234.79	5.616%	$247.9758	$247.98	$248.00	$248.00
7 purchase totals =	$1,268.72		$1,360.9501	$1,360.96	$1,361.00	$1,361.00