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	$55.34	8.212%	$59.8845	$59.88	$59.90	$59.90
Purchase #2	$85.88	12.505%	$96.6193	$96.62	$96.60	$96.60
Purchase #3	$151.73	12.644%	$170.9147	$170.91	$170.90	$170.90
Purchase #4	$7.54	11.206%	$8.3849	$8.38	$8.40	$8.40
Purchase #5	$213.37	12.288%	$239.5889	$239.59	$239.60	$239.60
Purchase #6	$211.35	6.471%	$225.0265	$225.03	$225.05	$225.00
Purchase #7	$230.64	10.772%	$255.4845	$255.48	$255.50	$255.50
7 purchase totals =	$955.85		$1,055.9033	$1,055.89	$1,055.95	$1,055.90