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	$50.48	10.448%	$55.7542	$55.75	$55.75	$55.80
Purchase #2	$29.26	8.797%	$31.834	$31.83	$31.85	$31.80
Purchase #3	$152.73	13.275%	$173.0049	$173.00	$173.00	$173.00
Purchase #4	$33.46	11.843%	$37.4227	$37.42	$37.40	$37.40
Purchase #5	$101.38	6.554%	$108.0244	$108.02	$108.00	$108.00
Purchase #6	$180.28	5.587%	$190.3522	$190.35	$190.35	$190.40
Purchase #7	$38.25	12.142%	$42.8943	$42.89	$42.90	$42.90
7 purchase totals =	$585.84		$639.2867	$639.26	$639.25	$639.30