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	$236.37	6.821%	$252.4928	$252.49	$252.50	$252.50
Purchase #2	$91.55	13.190%	$103.6254	$103.63	$103.65	$103.60
Purchase #3	$118.36	4.427%	$123.5998	$123.60	$123.60	$123.60
Purchase #4	$224.81	7.304%	$241.2301	$241.23	$241.25	$241.20
Purchase #5	$97.93	13.818%	$111.462	$111.46	$111.45	$111.50
Purchase #6	$72.41	13.133%	$81.9196	$81.92	$81.90	$81.90
Purchase #7	$83.88	12.623%	$94.4682	$94.47	$94.45	$94.50
7 purchase totals =	$925.31		$1,008.7979	$1,008.80	$1,008.80	$1,008.80