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	$49.85	13.674%	$56.6665	$56.67	$56.65	$56.70
Purchase #2	$183.66	12.297%	$206.2447	$206.24	$206.25	$206.20
Purchase #3	$162.70	11.870%	$182.0125	$182.01	$182.00	$182.00
Purchase #4	$178.35	3.180%	$184.0215	$184.02	$184.00	$184.00
Purchase #5	$159.25	13.453%	$180.6739	$180.67	$180.65	$180.70
Purchase #6	$104.50	6.705%	$111.5067	$111.51	$111.50	$111.50
Purchase #7	$168.56	12.797%	$190.1306	$190.13	$190.15	$190.10
7 purchase totals =	$1,006.87		$1,111.2564	$1,111.25	$1,111.20	$1,111.20