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	$160.74	11.771%	$179.6607	$179.66	$179.65	$179.70
Purchase #2	$71.78	13.132%	$81.2061	$81.21	$81.20	$81.20
Purchase #3	$91.34	12.839%	$103.0671	$103.07	$103.05	$103.10
Purchase #4	$52.35	13.424%	$59.3775	$59.38	$59.40	$59.40
Purchase #5	$219.59	4.545%	$229.5704	$229.57	$229.55	$229.60
Purchase #6	$40.49	8.506%	$43.9341	$43.93	$43.95	$43.90
Purchase #7	$123.41	9.179%	$134.7378	$134.74	$134.75	$134.70
7 purchase totals =	$759.70		$831.5537	$831.56	$831.55	$831.60