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	$36.92	12.130%	$41.3984	$41.40	$41.40	$41.40
Purchase #2	$55.60	11.613%	$62.0568	$62.06	$62.05	$62.10
Purchase #3	$150.71	9.624%	$165.2143	$165.21	$165.20	$165.20
Purchase #4	$248.50	8.482%	$269.5778	$269.58	$269.60	$269.60
Purchase #5	$156.85	12.526%	$176.497	$176.50	$176.50	$176.50
Purchase #6	$178.34	4.209%	$185.8463	$185.85	$185.85	$185.80
Purchase #7	$19.97	11.841%	$22.3346	$22.33	$22.35	$22.30
7 purchase totals =	$846.89		$922.9252	$922.93	$922.95	$922.90