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	$123.69	12.518%	$139.1735	$139.17	$139.15	$139.20
Purchase #2	$35.48	3.811%	$36.8321	$36.83	$36.85	$36.80
Purchase #3	$48.93	10.469%	$54.0525	$54.05	$54.05	$54.10
Purchase #4	$40.72	3.108%	$41.9856	$41.99	$42.00	$42.00
Purchase #5	$51.46	4.864%	$53.963	$53.96	$53.95	$54.00
Purchase #6	$178.52	7.693%	$192.2535	$192.25	$192.25	$192.30
Purchase #7	$47.31	10.254%	$52.1612	$52.16	$52.15	$52.20
7 purchase totals =	$526.11		$570.4214	$570.41	$570.40	$570.60