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	$125.86	8.357%	$136.3781	$136.38	$136.40	$136.40
Purchase #2	$170.80	8.565%	$185.429	$185.43	$185.45	$185.40
Purchase #3	$89.71	7.655%	$96.5773	$96.58	$96.60	$96.60
Purchase #4	$189.61	3.785%	$196.7867	$196.79	$196.80	$196.80
Purchase #5	$139.64	12.193%	$156.6663	$156.67	$156.65	$156.70
Purchase #6	$12.56	5.514%	$13.2526	$13.25	$13.25	$13.30
Purchase #7	$239.94	6.468%	$255.4593	$255.46	$255.45	$255.50
7 purchase totals =	$968.12		$1,040.5493	$1,040.56	$1,040.60	$1,040.70