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	$234.76	9.277%	$256.5387	$256.54	$256.55	$256.50
Purchase #2	$98.65	10.786%	$109.2904	$109.29	$109.30	$109.30
Purchase #3	$65.76	12.256%	$73.8195	$73.82	$73.80	$73.80
Purchase #4	$29.32	9.622%	$32.1412	$32.14	$32.15	$32.10
Purchase #5	$165.74	6.522%	$176.5496	$176.55	$176.55	$176.50
Purchase #6	$220.62	11.172%	$245.2677	$245.27	$245.25	$245.30
Purchase #7	$13.54	8.870%	$14.741	$14.74	$14.75	$14.70
7 purchase totals =	$828.39		$908.3481	$908.35	$908.35	$908.20