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	$39.59	13.138%	$44.7913	$44.79	$44.80	$44.80
Purchase #2	$91.55	13.654%	$104.0502	$104.05	$104.05	$104.10
Purchase #3	$124.84	4.287%	$130.1919	$130.19	$130.20	$130.20
Purchase #4	$82.73	9.304%	$90.4272	$90.43	$90.45	$90.40
Purchase #5	$91.46	5.522%	$96.5104	$96.51	$96.50	$96.50
Purchase #6	$46.80	6.857%	$50.0091	$50.01	$50.00	$50.00
Purchase #7	$204.98	8.332%	$222.0589	$222.06	$222.05	$222.10
7 purchase totals =	$681.95		$738.0390	$738.04	$738.05	$738.10