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	$80.74	11.497%	$90.0227	$90.02	$90.00	$90.00
Purchase #2	$219.92	7.873%	$237.2343	$237.23	$237.25	$237.20
Purchase #3	$243.60	7.743%	$262.4619	$262.46	$262.45	$262.50
Purchase #4	$21.32	13.483%	$24.1946	$24.19	$24.20	$24.20
Purchase #5	$172.65	13.705%	$196.3117	$196.31	$196.30	$196.30
Purchase #6	$116.82	4.705%	$122.3164	$122.32	$122.30	$122.30
Purchase #7	$35.32	12.291%	$39.6612	$39.66	$39.65	$39.70
7 purchase totals =	$890.37		$972.2028	$972.19	$972.15	$972.20