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	$63.81	6.329%	$67.8485	$67.85	$67.85	$67.80
Purchase #2	$226.41	10.721%	$250.6834	$250.68	$250.70	$250.70
Purchase #3	$29.64	13.291%	$33.5795	$33.58	$33.60	$33.60
Purchase #4	$99.54	5.545%	$105.0595	$105.06	$105.05	$105.10
Purchase #5	$38.33	12.292%	$43.0415	$43.04	$43.05	$43.00
Purchase #6	$72.52	13.820%	$82.5423	$82.54	$82.55	$82.50
Purchase #7	$66.54	11.125%	$73.9426	$73.94	$73.95	$73.90
7 purchase totals =	$596.79		$656.6973	$656.69	$656.75	$656.60