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	$119.32	3.624%	$123.6442	$123.64	$123.65	$123.60
Purchase #2	$137.29	10.194%	$151.2853	$151.29	$151.30	$151.30
Purchase #3	$238.51	5.624%	$251.9238	$251.92	$251.90	$251.90
Purchase #4	$100.54	9.766%	$110.3587	$110.36	$110.35	$110.40
Purchase #5	$121.91	7.464%	$131.0094	$131.01	$131.00	$131.00
Purchase #6	$23.69	8.639%	$25.7366	$25.74	$25.75	$25.70
Purchase #7	$107.28	3.477%	$111.0101	$111.01	$111.00	$111.00
7 purchase totals =	$848.54		$904.9681	$904.97	$904.95	$904.90