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	$77.85	4.174%	$81.0995	$81.10	$81.10	$81.10
Purchase #2	$109.59	13.530%	$124.4175	$124.42	$124.40	$124.40
Purchase #3	$103.82	5.583%	$109.6163	$109.62	$109.60	$109.60
Purchase #4	$105.88	12.387%	$118.9954	$119.00	$119.00	$119.00
Purchase #5	$56.67	9.632%	$62.1285	$62.13	$62.15	$62.10
Purchase #6	$159.31	5.350%	$167.8331	$167.83	$167.85	$167.80
Purchase #7	$78.82	8.394%	$85.4362	$85.44	$85.45	$85.40
7 purchase totals =	$691.94		$749.5265	$749.54	$749.55	$749.40