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	$127.69	9.540%	$139.8716	$139.87	$139.85	$139.90
Purchase #2	$232.53	4.448%	$242.8729	$242.87	$242.85	$242.90
Purchase #3	$153.44	12.517%	$172.6461	$172.65	$172.65	$172.60
Purchase #4	$234.98	5.448%	$247.7817	$247.78	$247.80	$247.80
Purchase #5	$14.34	3.791%	$14.8836	$14.88	$14.90	$14.90
Purchase #6	$200.82	12.766%	$226.4567	$226.46	$226.45	$226.50
Purchase #7	$91.74	5.632%	$96.9068	$96.91	$96.90	$96.90
7 purchase totals =	$1,055.54		$1,141.4194	$1,141.42	$1,141.40	$1,141.50