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	$127.72	3.514%	$132.2081	$132.21	$132.20	$132.20
Purchase #2	$182.25	5.400%	$192.0915	$192.09	$192.10	$192.10
Purchase #3	$29.90	9.532%	$32.7501	$32.75	$32.75	$32.80
Purchase #4	$89.66	12.506%	$100.8729	$100.87	$100.85	$100.90
Purchase #5	$52.36	13.502%	$59.4296	$59.43	$59.45	$59.40
Purchase #6	$145.93	3.353%	$150.823	$150.82	$150.80	$150.80
Purchase #7	$159.86	3.495%	$165.4471	$165.45	$165.45	$165.40
7 purchase totals =	$787.68		$833.6223	$833.62	$833.60	$833.60