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	$246.55	9.457%	$269.8662	$269.87	$269.85	$269.90
Purchase #2	$82.78	4.369%	$86.3967	$86.40	$86.40	$86.40
Purchase #3	$49.84	11.503%	$55.5731	$55.57	$55.55	$55.60
Purchase #4	$11.61	9.828%	$12.751	$12.75	$12.75	$12.80
Purchase #5	$112.89	4.794%	$118.3019	$118.30	$118.30	$118.30
Purchase #6	$131.73	3.382%	$136.1851	$136.19	$136.20	$136.20
Purchase #7	$178.78	3.761%	$185.5039	$185.50	$185.50	$185.50
7 purchase totals =	$814.18		$864.5779	$864.58	$864.55	$864.70