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	$6.87	10.174%	$7.569	$7.57	$7.55	$7.60
Purchase #2	$127.31	7.834%	$137.2835	$137.28	$137.30	$137.30
Purchase #3	$41.89	11.745%	$46.81	$46.81	$46.80	$46.80
Purchase #4	$206.38	9.835%	$226.6775	$226.68	$226.70	$226.70
Purchase #5	$149.59	12.638%	$168.4952	$168.50	$168.50	$168.50
Purchase #6	$54.42	9.176%	$59.4136	$59.41	$59.40	$59.40
Purchase #7	$99.27	12.725%	$111.9021	$111.90	$111.90	$111.90
7 purchase totals =	$685.73		$758.1509	$758.15	$758.15	$758.20