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	$164.81	13.398%	$186.8912	$186.89	$186.90	$186.90
Purchase #2	$164.58	12.308%	$184.8365	$184.84	$184.85	$184.80
Purchase #3	$202.52	3.104%	$208.8062	$208.81	$208.80	$208.80
Purchase #4	$31.87	3.251%	$32.9061	$32.91	$32.90	$32.90
Purchase #5	$112.61	7.388%	$120.9296	$120.93	$120.95	$120.90
Purchase #6	$138.52	4.317%	$144.4999	$144.50	$144.50	$144.50
Purchase #7	$54.82	7.724%	$59.0543	$59.05	$59.05	$59.10
7 purchase totals =	$869.73		$937.9238	$937.93	$937.95	$937.90