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	$132.72	5.778%	$140.3886	$140.39	$140.40	$140.40
Purchase #2	$29.41	13.164%	$33.2815	$33.28	$33.30	$33.30
Purchase #3	$103.61	7.655%	$111.5413	$111.54	$111.55	$111.50
Purchase #4	$57.28	5.529%	$60.447	$60.45	$60.45	$60.40
Purchase #5	$139.32	4.438%	$145.503	$145.50	$145.50	$145.50
Purchase #6	$249.34	7.302%	$267.5468	$267.55	$267.55	$267.50
Purchase #7	$248.94	13.111%	$281.5785	$281.58	$281.60	$281.60
7 purchase totals =	$960.62		$1,040.2867	$1,040.29	$1,040.35	$1,040.20