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	$78.55	5.508%	$82.8765	$82.88	$82.90	$82.90
Purchase #2	$66.33	13.312%	$75.1598	$75.16	$75.15	$75.20
Purchase #3	$161.56	3.666%	$167.4828	$167.48	$167.50	$167.50
Purchase #4	$113.51	9.664%	$124.4796	$124.48	$124.50	$124.50
Purchase #5	$121.80	5.485%	$128.4807	$128.48	$128.50	$128.50
Purchase #6	$169.30	12.782%	$190.9399	$190.94	$190.95	$190.90
Purchase #7	$229.47	8.499%	$248.9727	$248.97	$248.95	$249.00
7 purchase totals =	$940.52		$1,018.3920	$1,018.39	$1,018.45	$1,018.50