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	$151.38	8.306%	$163.9536	$163.95	$163.95	$164.00
Purchase #2	$125.69	10.691%	$139.1275	$139.13	$139.15	$139.10
Purchase #3	$97.38	3.425%	$100.7153	$100.72	$100.70	$100.70
Purchase #4	$78.50	11.229%	$87.3148	$87.31	$87.30	$87.30
Purchase #5	$165.39	9.506%	$181.112	$181.11	$181.10	$181.10
Purchase #6	$39.58	8.116%	$42.7923	$42.79	$42.80	$42.80
Purchase #7	$55.60	12.437%	$62.515	$62.52	$62.50	$62.50
7 purchase totals =	$713.52		$777.5305	$777.53	$777.50	$777.50