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	$35.64	4.240%	$37.1511	$37.15	$37.15	$37.20
Purchase #2	$210.59	5.556%	$222.2904	$222.29	$222.30	$222.30
Purchase #3	$125.82	10.487%	$139.0147	$139.01	$139.00	$139.00
Purchase #4	$164.89	11.818%	$184.3767	$184.38	$184.40	$184.40
Purchase #5	$173.50	6.364%	$184.5415	$184.54	$184.55	$184.50
Purchase #6	$226.94	5.282%	$238.927	$238.93	$238.95	$238.90
Purchase #7	$85.29	9.303%	$93.2245	$93.22	$93.20	$93.20
7 purchase totals =	$1,022.67		$1,099.5259	$1,099.52	$1,099.55	$1,099.50