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	$51.31	10.111%	$56.498	$56.50	$56.50	$56.50
Purchase #2	$74.51	11.478%	$83.0623	$83.06	$83.05	$83.10
Purchase #3	$70.91	6.426%	$75.4667	$75.47	$75.45	$75.50
Purchase #4	$36.61	13.423%	$41.5242	$41.52	$41.50	$41.50
Purchase #5	$31.57	12.105%	$35.3915	$35.39	$35.40	$35.40
Purchase #6	$139.51	3.535%	$144.4417	$144.44	$144.45	$144.40
Purchase #7	$144.88	9.701%	$158.9348	$158.93	$158.95	$158.90
7 purchase totals =	$549.30		$595.3192	$595.31	$595.30	$595.30