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	$129.50	11.366%	$144.219	$144.22	$144.20	$144.20
Purchase #2	$96.68	9.157%	$105.533	$105.53	$105.55	$105.50
Purchase #3	$164.57	13.108%	$186.1418	$186.14	$186.15	$186.10
Purchase #4	$148.82	10.511%	$164.4625	$164.46	$164.45	$164.50
Purchase #5	$26.82	7.694%	$28.8835	$28.88	$28.90	$28.90
Purchase #6	$196.65	13.122%	$222.4544	$222.45	$222.45	$222.50
Purchase #7	$148.70	12.263%	$166.9351	$166.94	$166.95	$166.90
7 purchase totals =	$911.74		$1,018.6293	$1,018.62	$1,018.65	$1,018.60