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	$145.45	6.837%	$155.3944	$155.39	$155.40	$155.40
Purchase #2	$205.32	4.785%	$215.1446	$215.14	$215.15	$215.10
Purchase #3	$169.71	9.176%	$185.2826	$185.28	$185.30	$185.30
Purchase #4	$82.92	13.176%	$93.8455	$93.85	$93.85	$93.80
Purchase #5	$216.60	10.526%	$239.3993	$239.40	$239.40	$239.40
Purchase #6	$192.55	3.723%	$199.7186	$199.72	$199.70	$199.70
Purchase #7	$95.56	4.751%	$100.1001	$100.10	$100.10	$100.10
7 purchase totals =	$1,108.11		$1,188.8851	$1,188.88	$1,188.90	$1,188.80