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	$87.25	3.854%	$90.6126	$90.61	$90.60	$90.60
Purchase #2	$38.54	10.865%	$42.7274	$42.73	$42.75	$42.70
Purchase #3	$149.89	8.715%	$162.9529	$162.95	$162.95	$163.00
Purchase #4	$88.46	10.690%	$97.9164	$97.92	$97.90	$97.90
Purchase #5	$234.27	5.213%	$246.4825	$246.48	$246.50	$246.50
Purchase #6	$172.42	12.448%	$193.8828	$193.88	$193.90	$193.90
Purchase #7	$121.83	4.350%	$127.1296	$127.13	$127.15	$127.10
7 purchase totals =	$892.66		$961.7042	$961.70	$961.75	$961.70