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	$23.32	6.705%	$24.8836	$24.88	$24.90	$24.90
Purchase #2	$104.85	3.312%	$108.3226	$108.32	$108.30	$108.30
Purchase #3	$38.47	10.396%	$42.4693	$42.47	$42.45	$42.50
Purchase #4	$52.64	12.518%	$59.2295	$59.23	$59.25	$59.20
Purchase #5	$195.25	13.612%	$221.8274	$221.83	$221.85	$221.80
Purchase #6	$106.77	8.237%	$115.5646	$115.56	$115.55	$115.60
Purchase #7	$114.49	5.833%	$121.1682	$121.17	$121.15	$121.20
7 purchase totals =	$635.79		$693.4652	$693.46	$693.45	$693.50