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	$240.86	3.527%	$249.3551	$249.36	$249.35	$249.40
Purchase #2	$228.88	6.597%	$243.9792	$243.98	$244.00	$244.00
Purchase #3	$178.89	6.542%	$190.593	$190.59	$190.60	$190.60
Purchase #4	$213.75	3.313%	$220.8315	$220.83	$220.85	$220.80
Purchase #5	$90.77	11.753%	$101.4382	$101.44	$101.45	$101.40
Purchase #6	$225.30	13.285%	$255.2311	$255.23	$255.25	$255.20
Purchase #7	$48.32	12.256%	$54.2421	$54.24	$54.25	$54.20
7 purchase totals =	$1,226.77		$1,315.6702	$1,315.67	$1,315.75	$1,315.60