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	$7.47	4.405%	$7.7991	$7.80	$7.80	$7.80
Purchase #2	$66.71	4.124%	$69.4611	$69.46	$69.45	$69.50
Purchase #3	$145.41	4.423%	$151.8415	$151.84	$151.85	$151.80
Purchase #4	$140.93	3.372%	$145.6822	$145.68	$145.70	$145.70
Purchase #5	$100.69	5.638%	$106.3669	$106.37	$106.35	$106.40
Purchase #6	$53.44	3.741%	$55.4392	$55.44	$55.45	$55.40
Purchase #7	$34.27	8.746%	$37.2673	$37.27	$37.25	$37.30
7 purchase totals =	$548.92		$573.8573	$573.86	$573.85	$573.90