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	$20.82	10.307%	$22.9659	$22.97	$22.95	$23.00
Purchase #2	$151.93	12.655%	$171.1567	$171.16	$171.15	$171.20
Purchase #3	$115.38	12.813%	$130.1636	$130.16	$130.15	$130.20
Purchase #4	$21.90	11.693%	$24.4608	$24.46	$24.45	$24.50
Purchase #5	$142.98	5.257%	$150.4965	$150.50	$150.50	$150.50
Purchase #6	$148.87	9.412%	$162.8816	$162.88	$162.90	$162.90
Purchase #7	$217.86	13.609%	$247.5086	$247.51	$247.50	$247.50
7 purchase totals =	$819.74		$909.6337	$909.64	$909.60	$909.80