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	$127.75	11.492%	$142.431	$142.43	$142.45	$142.40
Purchase #2	$205.66	5.382%	$216.7286	$216.73	$216.75	$216.70
Purchase #3	$141.59	13.384%	$160.5404	$160.54	$160.55	$160.50
Purchase #4	$87.35	8.597%	$94.8595	$94.86	$94.85	$94.90
Purchase #5	$100.53	11.276%	$111.8658	$111.87	$111.85	$111.90
Purchase #6	$88.99	3.376%	$91.9943	$91.99	$92.00	$92.00
Purchase #7	$36.55	6.221%	$38.8238	$38.82	$38.80	$38.80
7 purchase totals =	$788.42		$857.2434	$857.24	$857.25	$857.20