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	$8.35	6.663%	$8.9064	$8.91	$8.90	$8.90
Purchase #2	$152.45	6.563%	$162.4553	$162.46	$162.45	$162.50
Purchase #3	$84.34	6.393%	$89.7319	$89.73	$89.75	$89.70
Purchase #4	$29.32	3.255%	$30.2744	$30.27	$30.25	$30.30
Purchase #5	$217.43	5.178%	$228.6885	$228.69	$228.70	$228.70
Purchase #6	$6.94	13.387%	$7.8691	$7.87	$7.85	$7.90
Purchase #7	$172.64	13.591%	$196.1035	$196.10	$196.10	$196.10
7 purchase totals =	$671.47		$724.0291	$724.03	$724.00	$724.10