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	$225.87	13.150%	$255.5719	$255.57	$255.55	$255.60
Purchase #2	$27.50	5.623%	$29.0463	$29.05	$29.05	$29.00
Purchase #3	$44.78	13.538%	$50.8423	$50.84	$50.85	$50.80
Purchase #4	$79.34	12.616%	$89.3495	$89.35	$89.35	$89.30
Purchase #5	$40.89	12.277%	$45.9101	$45.91	$45.90	$45.90
Purchase #6	$38.27	13.669%	$43.5011	$43.50	$43.50	$43.50
Purchase #7	$50.59	10.660%	$55.9829	$55.98	$56.00	$56.00
7 purchase totals =	$507.24		$570.2041	$570.20	$570.20	$570.10