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	$250.49	11.734%	$279.8825	$279.88	$279.90	$279.90
Purchase #2	$234.53	12.800%	$264.5498	$264.55	$264.55	$264.50
Purchase #3	$121.92	4.372%	$127.2503	$127.25	$127.25	$127.30
Purchase #4	$148.53	8.185%	$160.6872	$160.69	$160.70	$160.70
Purchase #5	$14.80	7.180%	$15.8626	$15.86	$15.85	$15.90
Purchase #6	$239.85	11.790%	$268.1283	$268.13	$268.15	$268.10
Purchase #7	$131.38	9.387%	$143.7126	$143.71	$143.70	$143.70
7 purchase totals =	$1,141.50		$1,260.0733	$1,260.07	$1,260.10	$1,260.10