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	$50.89	6.196%	$54.0431	$54.04	$54.05	$54.00
Purchase #2	$160.61	4.841%	$168.3851	$168.39	$168.40	$168.40
Purchase #3	$18.62	7.316%	$19.9822	$19.98	$20.00	$20.00
Purchase #4	$13.50	9.501%	$14.7826	$14.78	$14.80	$14.80
Purchase #5	$42.89	6.119%	$45.5144	$45.51	$45.50	$45.50
Purchase #6	$121.96	12.277%	$136.933	$136.93	$136.95	$136.90
Purchase #7	$114.52	4.808%	$120.0261	$120.03	$120.05	$120.00
7 purchase totals =	$522.99		$559.6665	$559.66	$559.75	$559.60