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	$73.78	9.231%	$80.5906	$80.59	$80.60	$80.60
Purchase #2	$69.62	12.530%	$78.3434	$78.34	$78.35	$78.30
Purchase #3	$62.41	6.464%	$66.4442	$66.44	$66.45	$66.40
Purchase #4	$189.98	4.159%	$197.8813	$197.88	$197.90	$197.90
Purchase #5	$93.61	6.854%	$100.026	$100.03	$100.05	$100.00
Purchase #6	$117.76	11.605%	$131.426	$131.43	$131.45	$131.40
Purchase #7	$11.64	3.304%	$12.0246	$12.02	$12.00	$12.00
7 purchase totals =	$618.80		$666.7361	$666.73	$666.80	$666.60