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	$111.75	11.779%	$124.913	$124.91	$124.90	$124.90
Purchase #2	$56.97	3.862%	$59.1702	$59.17	$59.15	$59.20
Purchase #3	$12.46	6.295%	$13.2444	$13.24	$13.25	$13.20
Purchase #4	$108.90	3.871%	$113.1155	$113.12	$113.10	$113.10
Purchase #5	$38.54	10.318%	$42.5166	$42.52	$42.50	$42.50
Purchase #6	$172.64	11.353%	$192.2398	$192.24	$192.25	$192.20
Purchase #7	$5.39	11.712%	$6.0213	$6.02	$6.00	$6.00
7 purchase totals =	$506.65		$551.2208	$551.22	$551.15	$551.10