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	$104.88	3.487%	$108.5372	$108.54	$108.55	$108.50
Purchase #2	$169.88	12.872%	$191.747	$191.75	$191.75	$191.70
Purchase #3	$155.60	9.363%	$170.1688	$170.17	$170.15	$170.20
Purchase #4	$190.71	12.826%	$215.1705	$215.17	$215.15	$215.20
Purchase #5	$130.81	7.480%	$140.5946	$140.59	$140.60	$140.60
Purchase #6	$69.97	4.127%	$72.8577	$72.86	$72.85	$72.90
Purchase #7	$175.80	8.351%	$190.4811	$190.48	$190.50	$190.50
7 purchase totals =	$997.65		$1,089.5569	$1,089.56	$1,089.55	$1,089.60