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	$5.85	7.744%	$6.303	$6.30	$6.30	$6.30
Purchase #2	$36.93	12.722%	$41.6282	$41.63	$41.65	$41.60
Purchase #3	$117.67	13.175%	$133.173	$133.17	$133.15	$133.20
Purchase #4	$88.28	4.782%	$92.5015	$92.50	$92.50	$92.50
Purchase #5	$205.53	11.405%	$228.9707	$228.97	$228.95	$229.00
Purchase #6	$53.50	5.565%	$56.4773	$56.48	$56.50	$56.50
Purchase #7	$78.89	13.528%	$89.5622	$89.56	$89.55	$89.60
7 purchase totals =	$586.65		$648.6159	$648.61	$648.60	$648.70