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	$107.98	3.210%	$111.4462	$111.45	$111.45	$111.40
Purchase #2	$196.26	12.564%	$220.9181	$220.92	$220.90	$220.90
Purchase #3	$124.70	11.848%	$139.4745	$139.47	$139.45	$139.50
Purchase #4	$125.46	13.588%	$142.5075	$142.51	$142.50	$142.50
Purchase #5	$182.47	13.302%	$206.7422	$206.74	$206.75	$206.70
Purchase #6	$116.51	13.596%	$132.3507	$132.35	$132.35	$132.40
Purchase #7	$86.79	13.442%	$98.4563	$98.46	$98.45	$98.50
7 purchase totals =	$940.17		$1,051.8955	$1,051.90	$1,051.85	$1,051.90