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	$35.36	13.478%	$40.1258	$40.13	$40.15	$40.10
Purchase #2	$81.66	11.373%	$90.9472	$90.95	$90.95	$90.90
Purchase #3	$68.38	9.501%	$74.8768	$74.88	$74.90	$74.90
Purchase #4	$193.80	8.858%	$210.9668	$210.97	$210.95	$211.00
Purchase #5	$99.81	4.428%	$104.2296	$104.23	$104.25	$104.20
Purchase #6	$125.99	12.644%	$141.9202	$141.92	$141.90	$141.90
Purchase #7	$143.91	10.842%	$159.5127	$159.51	$159.50	$159.50
7 purchase totals =	$748.91		$822.5791	$822.59	$822.60	$822.50