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	$51.57	10.707%	$57.0916	$57.09	$57.10	$57.10
Purchase #2	$32.92	10.479%	$36.3697	$36.37	$36.35	$36.40
Purchase #3	$100.58	3.723%	$104.3246	$104.32	$104.30	$104.30
Purchase #4	$108.34	3.592%	$112.2316	$112.23	$112.25	$112.20
Purchase #5	$209.34	10.679%	$231.6954	$231.70	$231.70	$231.70
Purchase #6	$116.78	9.721%	$128.1322	$128.13	$128.15	$128.10
Purchase #7	$55.25	8.381%	$59.8805	$59.88	$59.90	$59.90
7 purchase totals =	$674.78		$729.7256	$729.72	$729.75	$729.70