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	$136.70	4.165%	$142.3936	$142.39	$142.40	$142.40
Purchase #2	$102.83	8.795%	$111.8739	$111.87	$111.85	$111.90
Purchase #3	$19.82	7.175%	$21.2421	$21.24	$21.25	$21.20
Purchase #4	$209.92	7.120%	$224.8663	$224.87	$224.85	$224.90
Purchase #5	$85.78	11.716%	$95.83	$95.83	$95.85	$95.80
Purchase #6	$126.57	10.802%	$140.2421	$140.24	$140.25	$140.20
Purchase #7	$226.43	11.158%	$251.6951	$251.70	$251.70	$251.70
7 purchase totals =	$908.05		$988.1431	$988.14	$988.15	$988.10