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	$157.69	5.440%	$166.2683	$166.27	$166.25	$166.30
Purchase #2	$174.71	10.483%	$193.0248	$193.02	$193.00	$193.00
Purchase #3	$99.72	13.780%	$113.4614	$113.46	$113.45	$113.50
Purchase #4	$171.90	4.676%	$179.938	$179.94	$179.95	$179.90
Purchase #5	$10.73	6.611%	$11.4394	$11.44	$11.45	$11.40
Purchase #6	$250.94	11.458%	$279.6927	$279.69	$279.70	$279.70
Purchase #7	$179.75	11.150%	$199.7921	$199.79	$199.80	$199.80
7 purchase totals =	$1,045.44		$1,143.6167	$1,143.61	$1,143.60	$1,143.60