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	$243.37	12.340%	$273.4019	$273.40	$273.40	$273.40
Purchase #2	$153.90	8.243%	$166.586	$166.59	$166.60	$166.60
Purchase #3	$168.77	4.425%	$176.2381	$176.24	$176.25	$176.20
Purchase #4	$175.77	7.746%	$189.3851	$189.39	$189.40	$189.40
Purchase #5	$108.65	3.383%	$112.3256	$112.33	$112.35	$112.30
Purchase #6	$95.77	4.643%	$100.2166	$100.22	$100.20	$100.20
Purchase #7	$37.90	4.779%	$39.7112	$39.71	$39.70	$39.70
7 purchase totals =	$984.13		$1,057.8645	$1,057.88	$1,057.90	$1,057.80