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	$128.72	10.567%	$142.3218	$142.32	$142.30	$142.30
Purchase #2	$163.77	4.720%	$171.4999	$171.50	$171.50	$171.50
Purchase #3	$11.53	3.197%	$11.8986	$11.90	$11.90	$11.90
Purchase #4	$155.45	7.167%	$166.5911	$166.59	$166.60	$166.60
Purchase #5	$28.76	7.300%	$30.8595	$30.86	$30.85	$30.90
Purchase #6	$171.64	13.194%	$194.2862	$194.29	$194.30	$194.30
Purchase #7	$107.59	10.817%	$119.228	$119.23	$119.25	$119.20
7 purchase totals =	$767.46		$836.6851	$836.69	$836.70	$836.70