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	$199.62	12.655%	$224.8819	$224.88	$224.90	$224.90
Purchase #2	$230.78	7.624%	$248.3747	$248.37	$248.35	$248.40
Purchase #3	$127.60	13.150%	$144.3794	$144.38	$144.40	$144.40
Purchase #4	$103.87	9.356%	$113.5881	$113.59	$113.60	$113.60
Purchase #5	$36.61	13.123%	$41.4143	$41.41	$41.40	$41.40
Purchase #6	$84.81	8.642%	$92.1393	$92.14	$92.15	$92.10
Purchase #7	$112.48	3.424%	$116.3313	$116.33	$116.35	$116.30
7 purchase totals =	$895.77		$981.1090	$981.10	$981.15	$981.10