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	$75.44	11.225%	$83.9081	$83.91	$83.90	$83.90
Purchase #2	$159.43	12.372%	$179.1547	$179.15	$179.15	$179.20
Purchase #3	$98.38	5.349%	$103.6423	$103.64	$103.65	$103.60
Purchase #4	$39.94	8.807%	$43.4575	$43.46	$43.45	$43.50
Purchase #5	$107.71	3.664%	$111.6565	$111.66	$111.65	$111.70
Purchase #6	$47.48	6.267%	$50.4556	$50.46	$50.45	$50.50
Purchase #7	$246.84	5.738%	$261.0037	$261.00	$261.00	$261.00
7 purchase totals =	$775.22		$833.2784	$833.28	$833.25	$833.40