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	$150.31	10.408%	$165.9543	$165.95	$165.95	$166.00
Purchase #2	$102.81	8.395%	$111.4409	$111.44	$111.45	$111.40
Purchase #3	$152.96	8.206%	$165.5119	$165.51	$165.50	$165.50
Purchase #4	$99.85	10.135%	$109.9698	$109.97	$109.95	$110.00
Purchase #5	$75.51	4.470%	$78.8853	$78.89	$78.90	$78.90
Purchase #6	$168.93	10.494%	$186.6575	$186.66	$186.65	$186.70
Purchase #7	$104.98	9.383%	$114.8303	$114.83	$114.85	$114.80
7 purchase totals =	$855.35		$933.2500	$933.25	$933.25	$933.30