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	$102.47	3.358%	$105.9109	$105.91	$105.90	$105.90
Purchase #2	$36.73	9.632%	$40.2678	$40.27	$40.25	$40.30
Purchase #3	$103.80	9.304%	$113.4576	$113.46	$113.45	$113.50
Purchase #4	$222.89	9.762%	$244.6485	$244.65	$244.65	$244.60
Purchase #5	$60.75	9.154%	$66.3111	$66.31	$66.30	$66.30
Purchase #6	$230.44	9.331%	$251.9424	$251.94	$251.95	$251.90
Purchase #7	$108.94	7.779%	$117.4144	$117.41	$117.40	$117.40
7 purchase totals =	$866.02		$939.9527	$939.95	$939.90	$939.90