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	$29.54	11.840%	$33.0375	$33.04	$33.05	$33.00
Purchase #2	$210.36	3.541%	$217.8088	$217.81	$217.80	$217.80
Purchase #3	$85.94	4.436%	$89.7523	$89.75	$89.75	$89.80
Purchase #4	$92.68	8.416%	$100.4799	$100.48	$100.50	$100.50
Purchase #5	$66.60	7.702%	$71.7295	$71.73	$71.75	$71.70
Purchase #6	$43.58	9.470%	$47.707	$47.71	$47.70	$47.70
Purchase #7	$142.33	9.205%	$155.4315	$155.43	$155.45	$155.40
7 purchase totals =	$671.03		$715.9465	$715.95	$716.00	$715.90