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	$12.95	4.114%	$13.4828	$13.48	$13.50	$13.50
Purchase #2	$124.90	11.418%	$139.1611	$139.16	$139.15	$139.20
Purchase #3	$171.93	11.550%	$191.7879	$191.79	$191.80	$191.80
Purchase #4	$72.26	13.794%	$82.2275	$82.23	$82.25	$82.20
Purchase #5	$234.34	9.116%	$255.7024	$255.70	$255.70	$255.70
Purchase #6	$234.87	6.482%	$250.0943	$250.09	$250.10	$250.10
Purchase #7	$123.79	7.315%	$132.8452	$132.85	$132.85	$132.80
7 purchase totals =	$975.04		$1,065.3012	$1,065.30	$1,065.35	$1,065.30