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	$55.32	8.293%	$59.9077	$59.91	$59.90	$59.90
Purchase #2	$127.90	12.834%	$144.3147	$144.31	$144.30	$144.30
Purchase #3	$98.59	9.835%	$108.2863	$108.29	$108.30	$108.30
Purchase #4	$72.36	4.150%	$75.3629	$75.36	$75.35	$75.40
Purchase #5	$19.80	3.572%	$20.5073	$20.51	$20.50	$20.50
Purchase #6	$12.60	7.578%	$13.5548	$13.55	$13.55	$13.60
Purchase #7	$105.72	8.789%	$115.0117	$115.01	$115.00	$115.00
7 purchase totals =	$492.29		$536.9454	$536.94	$536.90	$537.00