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	$28.95	3.272%	$29.8972	$29.90	$29.90	$29.90
Purchase #2	$38.47	11.110%	$42.744	$42.74	$42.75	$42.70
Purchase #3	$133.77	8.109%	$144.6174	$144.62	$144.60	$144.60
Purchase #4	$130.34	7.302%	$139.8574	$139.86	$139.85	$139.90
Purchase #5	$24.62	12.159%	$27.6135	$27.61	$27.60	$27.60
Purchase #6	$196.72	9.135%	$214.6904	$214.69	$214.70	$214.70
Purchase #7	$248.47	12.326%	$279.0964	$279.10	$279.10	$279.10
7 purchase totals =	$801.34		$878.5163	$878.52	$878.50	$878.50