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	$51.52	7.826%	$55.552	$55.55	$55.55	$55.60
Purchase #2	$145.82	12.780%	$164.4558	$164.46	$164.45	$164.50
Purchase #3	$150.68	13.470%	$170.9766	$170.98	$171.00	$171.00
Purchase #4	$151.97	10.339%	$167.6822	$167.68	$167.70	$167.70
Purchase #5	$33.49	6.740%	$35.7472	$35.75	$35.75	$35.70
Purchase #6	$103.74	8.230%	$112.2778	$112.28	$112.30	$112.30
Purchase #7	$130.82	11.493%	$145.8551	$145.86	$145.85	$145.90
7 purchase totals =	$768.04		$852.5467	$852.56	$852.60	$852.70