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	$230.36	8.594%	$250.1571	$250.16	$250.15	$250.20
Purchase #2	$163.52	5.401%	$172.3517	$172.35	$172.35	$172.40
Purchase #3	$104.53	4.714%	$109.4575	$109.46	$109.45	$109.50
Purchase #4	$109.33	7.161%	$117.1591	$117.16	$117.15	$117.20
Purchase #5	$220.27	13.166%	$249.2707	$249.27	$249.25	$249.30
Purchase #6	$121.60	8.190%	$131.559	$131.56	$131.55	$131.60
Purchase #7	$179.88	8.529%	$195.222	$195.22	$195.20	$195.20
7 purchase totals =	$1,129.49		$1,225.1771	$1,225.18	$1,225.10	$1,225.40