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	$47.45	7.280%	$50.9044	$50.90	$50.90	$50.90
Purchase #2	$230.57	9.630%	$252.7739	$252.77	$252.75	$252.80
Purchase #3	$79.88	13.249%	$90.4633	$90.46	$90.45	$90.50
Purchase #4	$175.56	5.819%	$185.7758	$185.78	$185.80	$185.80
Purchase #5	$161.61	4.728%	$169.2509	$169.25	$169.25	$169.30
Purchase #6	$190.54	7.793%	$205.3888	$205.39	$205.40	$205.40
Purchase #7	$60.70	8.389%	$65.7921	$65.79	$65.80	$65.80
7 purchase totals =	$946.31		$1,020.3492	$1,020.34	$1,020.35	$1,020.50