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	$92.89	8.371%	$100.6658	$100.67	$100.65	$100.70
Purchase #2	$86.53	13.355%	$98.0861	$98.09	$98.10	$98.10
Purchase #3	$64.84	4.122%	$67.5127	$67.51	$67.50	$67.50
Purchase #4	$12.61	8.153%	$13.6381	$13.64	$13.65	$13.60
Purchase #5	$9.33	11.824%	$10.4332	$10.43	$10.45	$10.40
Purchase #6	$57.95	10.225%	$63.8754	$63.88	$63.90	$63.90
Purchase #7	$223.75	8.716%	$243.2521	$243.25	$243.25	$243.30
7 purchase totals =	$547.90		$597.4634	$597.47	$597.50	$597.50