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	$113.40	9.137%	$123.7614	$123.76	$123.75	$123.80
Purchase #2	$91.65	12.742%	$103.328	$103.33	$103.35	$103.30
Purchase #3	$24.40	10.661%	$27.0013	$27.00	$27.00	$27.00
Purchase #4	$248.92	8.157%	$269.2244	$269.22	$269.20	$269.20
Purchase #5	$147.50	11.267%	$164.1188	$164.12	$164.10	$164.10
Purchase #6	$218.40	5.460%	$230.3246	$230.32	$230.30	$230.30
Purchase #7	$85.99	5.151%	$90.4193	$90.42	$90.40	$90.40
7 purchase totals =	$930.26		$1,008.1778	$1,008.17	$1,008.10	$1,008.10