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	$54.32	3.296%	$56.1104	$56.11	$56.10	$56.10
Purchase #2	$155.45	7.352%	$166.8787	$166.88	$166.90	$166.90
Purchase #3	$102.56	10.400%	$113.2262	$113.23	$113.25	$113.20
Purchase #4	$56.69	4.311%	$59.1339	$59.13	$59.15	$59.10
Purchase #5	$192.40	11.512%	$214.5491	$214.55	$214.55	$214.50
Purchase #6	$136.89	11.825%	$153.0772	$153.08	$153.10	$153.10
Purchase #7	$79.46	5.325%	$83.6912	$83.69	$83.70	$83.70
7 purchase totals =	$777.77		$846.6667	$846.67	$846.75	$846.60