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	$141.35	12.768%	$159.3976	$159.40	$159.40	$159.40
Purchase #2	$37.77	8.530%	$40.9918	$40.99	$41.00	$41.00
Purchase #3	$124.95	11.567%	$139.403	$139.40	$139.40	$139.40
Purchase #4	$200.60	4.373%	$209.3722	$209.37	$209.35	$209.40
Purchase #5	$87.75	3.799%	$91.0836	$91.08	$91.10	$91.10
Purchase #6	$158.76	4.142%	$165.3358	$165.34	$165.35	$165.30
Purchase #7	$242.98	7.364%	$260.873	$260.87	$260.85	$260.90
7 purchase totals =	$994.16		$1,066.4570	$1,066.45	$1,066.45	$1,066.50