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	$206.73	7.574%	$222.3877	$222.39	$222.40	$222.40
Purchase #2	$230.95	5.200%	$242.9594	$242.96	$242.95	$243.00
Purchase #3	$24.52	11.144%	$27.2525	$27.25	$27.25	$27.30
Purchase #4	$140.67	9.106%	$153.4794	$153.48	$153.50	$153.50
Purchase #5	$230.51	10.632%	$255.0178	$255.02	$255.00	$255.00
Purchase #6	$128.50	10.275%	$141.7034	$141.70	$141.70	$141.70
Purchase #7	$31.69	11.654%	$35.3832	$35.38	$35.40	$35.40
7 purchase totals =	$993.57		$1,078.1834	$1,078.18	$1,078.20	$1,078.30