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	$19.32	11.870%	$21.6133	$21.61	$21.60	$21.60
Purchase #2	$6.46	6.360%	$6.8709	$6.87	$6.85	$6.90
Purchase #3	$70.70	11.709%	$78.9783	$78.98	$79.00	$79.00
Purchase #4	$159.50	4.749%	$167.0747	$167.07	$167.05	$167.10
Purchase #5	$30.66	5.398%	$32.315	$32.32	$32.30	$32.30
Purchase #6	$84.95	5.397%	$89.5348	$89.53	$89.55	$89.50
Purchase #7	$29.72	4.365%	$31.0173	$31.02	$31.00	$31.00
7 purchase totals =	$401.31		$427.4043	$427.40	$427.35	$427.40