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	$226.73	13.410%	$257.1345	$257.13	$257.15	$257.10
Purchase #2	$194.35	11.832%	$217.3455	$217.35	$217.35	$217.30
Purchase #3	$89.43	10.736%	$99.0312	$99.03	$99.05	$99.00
Purchase #4	$180.90	3.209%	$186.7051	$186.71	$186.70	$186.70
Purchase #5	$65.73	7.320%	$70.5414	$70.54	$70.55	$70.50
Purchase #6	$126.87	7.539%	$136.4347	$136.43	$136.45	$136.40
Purchase #7	$99.61	5.709%	$105.2967	$105.30	$105.30	$105.30
7 purchase totals =	$983.62		$1,072.4891	$1,072.49	$1,072.55	$1,072.30