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	$179.42	5.655%	$189.5662	$189.57	$189.55	$189.60
Purchase #2	$114.54	5.410%	$120.7366	$120.74	$120.75	$120.70
Purchase #3	$134.35	6.385%	$142.9282	$142.93	$142.95	$142.90
Purchase #4	$157.94	9.128%	$172.3568	$172.36	$172.35	$172.40
Purchase #5	$97.58	11.753%	$109.0486	$109.05	$109.05	$109.00
Purchase #6	$83.32	8.364%	$90.2889	$90.29	$90.30	$90.30
Purchase #7	$52.69	7.361%	$56.5685	$56.57	$56.55	$56.60
7 purchase totals =	$819.84		$881.4938	$881.51	$881.50	$881.50