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	$7.46	12.361%	$8.3821	$8.38	$8.40	$8.40
Purchase #2	$155.82	5.451%	$164.3137	$164.31	$164.30	$164.30
Purchase #3	$192.32	5.688%	$203.2592	$203.26	$203.25	$203.30
Purchase #4	$19.52	5.482%	$20.5901	$20.59	$20.60	$20.60
Purchase #5	$70.56	3.433%	$72.9823	$72.98	$73.00	$73.00
Purchase #6	$219.46	13.194%	$248.4156	$248.42	$248.40	$248.40
Purchase #7	$247.59	11.269%	$275.4909	$275.49	$275.50	$275.50
7 purchase totals =	$912.73		$993.4339	$993.43	$993.45	$993.50