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	$143.46	8.593%	$155.7875	$155.79	$155.80	$155.80
Purchase #2	$23.34	9.789%	$25.6248	$25.62	$25.60	$25.60
Purchase #3	$20.36	11.314%	$22.6635	$22.66	$22.65	$22.70
Purchase #4	$150.50	11.421%	$167.6886	$167.69	$167.70	$167.70
Purchase #5	$80.99	12.182%	$90.8562	$90.86	$90.85	$90.90
Purchase #6	$127.38	3.103%	$131.3326	$131.33	$131.35	$131.30
Purchase #7	$47.42	7.398%	$50.9281	$50.93	$50.95	$50.90
7 purchase totals =	$593.45		$644.8813	$644.88	$644.90	$644.90