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	$163.54	5.362%	$172.309	$172.31	$172.30	$172.30
Purchase #2	$79.70	7.358%	$85.5643	$85.56	$85.55	$85.60
Purchase #3	$24.92	9.572%	$27.3053	$27.31	$27.30	$27.30
Purchase #4	$161.42	11.486%	$179.9607	$179.96	$179.95	$180.00
Purchase #5	$15.60	10.380%	$17.2193	$17.22	$17.20	$17.20
Purchase #6	$115.42	10.472%	$127.5068	$127.51	$127.50	$127.50
Purchase #7	$162.53	11.506%	$181.2307	$181.23	$181.25	$181.20
7 purchase totals =	$723.13		$791.0961	$791.10	$791.05	$791.10