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	$47.72	5.612%	$50.398	$50.40	$50.40	$50.40
Purchase #2	$27.41	10.417%	$30.2653	$30.27	$30.25	$30.30
Purchase #3	$39.63	13.285%	$44.8948	$44.89	$44.90	$44.90
Purchase #4	$235.77	12.620%	$265.5242	$265.52	$265.50	$265.50
Purchase #5	$64.97	11.476%	$72.426	$72.43	$72.45	$72.40
Purchase #6	$64.48	3.869%	$66.9747	$66.97	$66.95	$67.00
Purchase #7	$157.52	13.698%	$179.0971	$179.10	$179.10	$179.10
7 purchase totals =	$637.50		$709.5801	$709.58	$709.55	$709.60