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	$164.74	3.862%	$171.1023	$171.10	$171.10	$171.10
Purchase #2	$65.43	10.586%	$72.3564	$72.36	$72.35	$72.40
Purchase #3	$26.44	11.716%	$29.5377	$29.54	$29.55	$29.50
Purchase #4	$110.88	11.306%	$123.4161	$123.42	$123.40	$123.40
Purchase #5	$42.41	13.226%	$48.0191	$48.02	$48.00	$48.00
Purchase #6	$105.54	5.174%	$111.0006	$111.00	$111.00	$111.00
Purchase #7	$117.87	4.778%	$123.5018	$123.50	$123.50	$123.50
7 purchase totals =	$633.31		$678.9340	$678.94	$678.90	$678.90