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	$166.83	3.631%	$172.8876	$172.89	$172.90	$172.90
Purchase #2	$151.50	9.304%	$165.5956	$165.60	$165.60	$165.60
Purchase #3	$15.25	4.163%	$15.8849	$15.88	$15.90	$15.90
Purchase #4	$139.37	9.155%	$152.1293	$152.13	$152.15	$152.10
Purchase #5	$224.61	11.547%	$250.5457	$250.55	$250.55	$250.50
Purchase #6	$168.30	5.817%	$178.09	$178.09	$178.10	$178.10
Purchase #7	$221.67	8.278%	$240.0198	$240.02	$240.00	$240.00
7 purchase totals =	$1,087.53		$1,175.1529	$1,175.16	$1,175.20	$1,175.10