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	$47.56	6.632%	$50.7142	$50.71	$50.70	$50.70
Purchase #2	$156.90	13.739%	$178.4565	$178.46	$178.45	$178.50
Purchase #3	$225.60	5.592%	$238.2156	$238.22	$238.20	$238.20
Purchase #4	$79.26	5.186%	$83.3704	$83.37	$83.35	$83.40
Purchase #5	$66.33	9.411%	$72.5723	$72.57	$72.55	$72.60
Purchase #6	$179.86	10.729%	$199.1572	$199.16	$199.15	$199.20
Purchase #7	$55.40	4.263%	$57.7617	$57.76	$57.75	$57.80
7 purchase totals =	$810.91		$880.2479	$880.25	$880.15	$880.40