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	$45.42	9.810%	$49.8757	$49.88	$49.90	$49.90
Purchase #2	$148.44	6.742%	$158.4478	$158.45	$158.45	$158.40
Purchase #3	$40.82	9.691%	$44.7759	$44.78	$44.80	$44.80
Purchase #4	$54.86	3.662%	$56.869	$56.87	$56.85	$56.90
Purchase #5	$206.46	4.498%	$215.7466	$215.75	$215.75	$215.70
Purchase #6	$73.35	9.867%	$80.5874	$80.59	$80.60	$80.60
Purchase #7	$233.93	13.196%	$264.7994	$264.80	$264.80	$264.80
7 purchase totals =	$803.28		$871.1018	$871.12	$871.15	$871.10