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	$99.45	8.116%	$107.5214	$107.52	$107.50	$107.50
Purchase #2	$146.45	4.207%	$152.6112	$152.61	$152.60	$152.60
Purchase #3	$167.72	4.626%	$175.4787	$175.48	$175.50	$175.50
Purchase #4	$13.34	9.810%	$14.6487	$14.65	$14.65	$14.60
Purchase #5	$33.79	6.113%	$35.8556	$35.86	$35.85	$35.90
Purchase #6	$134.45	8.289%	$145.5946	$145.59	$145.60	$145.60
Purchase #7	$118.65	12.290%	$133.2321	$133.23	$133.25	$133.20
7 purchase totals =	$713.85		$764.9423	$764.94	$764.95	$764.90