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	$120.29	8.811%	$130.8888	$130.89	$130.90	$130.90
Purchase #2	$215.90	5.609%	$228.0098	$228.01	$228.00	$228.00
Purchase #3	$205.28	10.535%	$226.9062	$226.91	$226.90	$226.90
Purchase #4	$222.77	11.563%	$248.5289	$248.53	$248.55	$248.50
Purchase #5	$229.82	6.291%	$244.278	$244.28	$244.30	$244.30
Purchase #6	$56.27	6.414%	$59.8792	$59.88	$59.90	$59.90
Purchase #7	$5.72	3.211%	$5.9037	$5.90	$5.90	$5.90
7 purchase totals =	$1,056.05		$1,144.3946	$1,144.40	$1,144.45	$1,144.40