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	$239.87	3.868%	$249.1482	$249.15	$249.15	$249.10
Purchase #2	$38.51	10.464%	$42.5397	$42.54	$42.55	$42.50
Purchase #3	$186.72	6.201%	$198.2985	$198.30	$198.30	$198.30
Purchase #4	$88.36	10.439%	$97.5839	$97.58	$97.60	$97.60
Purchase #5	$219.61	8.633%	$238.5689	$238.57	$238.55	$238.60
Purchase #6	$139.60	9.158%	$152.3846	$152.38	$152.40	$152.40
Purchase #7	$229.84	11.773%	$256.8991	$256.90	$256.90	$256.90
7 purchase totals =	$1,142.51		$1,235.4229	$1,235.42	$1,235.45	$1,235.40