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	$39.91	8.812%	$43.4269	$43.43	$43.45	$43.40
Purchase #2	$208.60	11.668%	$232.9394	$232.94	$232.95	$232.90
Purchase #3	$215.52	10.109%	$237.3069	$237.31	$237.30	$237.30
Purchase #4	$152.51	8.527%	$165.5145	$165.51	$165.50	$165.50
Purchase #5	$28.79	4.752%	$30.1581	$30.16	$30.15	$30.20
Purchase #6	$64.75	11.609%	$72.2668	$72.27	$72.25	$72.30
Purchase #7	$143.68	4.773%	$150.5378	$150.54	$150.55	$150.50
7 purchase totals =	$853.76		$932.1504	$932.16	$932.15	$932.10