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	$93.44	10.411%	$103.168	$103.17	$103.15	$103.20
Purchase #2	$139.50	12.504%	$156.9431	$156.94	$156.95	$156.90
Purchase #3	$121.26	6.807%	$129.5142	$129.51	$129.50	$129.50
Purchase #4	$38.32	4.351%	$39.9873	$39.99	$40.00	$40.00
Purchase #5	$11.61	10.712%	$12.8537	$12.85	$12.85	$12.90
Purchase #6	$95.57	5.360%	$100.6926	$100.69	$100.70	$100.70
Purchase #7	$133.59	9.535%	$146.3278	$146.33	$146.35	$146.30
7 purchase totals =	$633.29		$689.4867	$689.48	$689.50	$689.50