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	$19.82	9.265%	$21.6563	$21.66	$21.65	$21.70
Purchase #2	$49.30	5.350%	$51.9376	$51.94	$51.95	$51.90
Purchase #3	$144.49	12.123%	$162.0065	$162.01	$162.00	$162.00
Purchase #4	$237.47	5.602%	$250.7731	$250.77	$250.75	$250.80
Purchase #5	$163.53	7.326%	$175.5102	$175.51	$175.50	$175.50
Purchase #6	$54.84	12.643%	$61.7734	$61.77	$61.75	$61.80
Purchase #7	$165.68	12.200%	$185.893	$185.89	$185.90	$185.90
7 purchase totals =	$835.13		$909.5501	$909.55	$909.50	$909.60