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	$134.74	3.575%	$139.557	$139.56	$139.55	$139.60
Purchase #2	$161.99	4.397%	$169.1127	$169.11	$169.10	$169.10
Purchase #3	$155.40	6.324%	$165.2275	$165.23	$165.25	$165.20
Purchase #4	$231.79	10.719%	$256.6356	$256.64	$256.65	$256.60
Purchase #5	$131.87	13.459%	$149.6184	$149.62	$149.60	$149.60
Purchase #6	$97.35	3.440%	$100.6988	$100.70	$100.70	$100.70
Purchase #7	$105.39	13.641%	$119.7662	$119.77	$119.75	$119.80
7 purchase totals =	$1,018.53		$1,100.6162	$1,100.63	$1,100.60	$1,100.60